Testing for a battery drain
Discussion
The battery on my car keeps draining itself and going flat. I need to test what the drain is on the battery, I'm pretty sure it's a multimeter that I need to do this. Would this one be ok?
http://www.machinemart.co.uk/shop/product/details/...
Also if anyone knows of a good guide showing how to do this and what everything means I'd appreciate it.
http://www.machinemart.co.uk/shop/product/details/...
Also if anyone knows of a good guide showing how to do this and what everything means I'd appreciate it.
V8mate said:
The battery on my track car goes flat in about a week.
Out of interest, once you have this meter, what are you going to do with it to identify the source of the drain?
Well the aftermarket connector for the steering wheel controls have stopped working recently but I don't know if that was a result of the flat battery (it didn't actually go completely flat though) and the alarm is notoriously temperamental. So I'd like to be able to isolate where it's coming from (if the drain is even too high at all). Out of interest, once you have this meter, what are you going to do with it to identify the source of the drain?
That meter will be fine.
You can disconnect the +ve terminal from the battery and then connect the multimeter between the cable and the battery +ve; making sure the meter is in DC current mode and the cables are in the correct sockets.
DO NOT START THE CAR or something will burn.
Remember that in a lot of modern cars control units and such will take a while to shut down - and possibly be restarted by doors opening etc, if possible you should rig it up so that you can take a reading without opening the car at all.
Aftermarket stereo? Is it wired up correctly?
You can disconnect the +ve terminal from the battery and then connect the multimeter between the cable and the battery +ve; making sure the meter is in DC current mode and the cables are in the correct sockets.
DO NOT START THE CAR or something will burn.
Remember that in a lot of modern cars control units and such will take a while to shut down - and possibly be restarted by doors opening etc, if possible you should rig it up so that you can take a reading without opening the car at all.
Aftermarket stereo? Is it wired up correctly?
Edited by john_p on Wednesday 29th September 11:53
john_p said:
You can disconnect the +ve terminal from the battery and then connect the multimeter between the cable and the battery +ve; making sure the meter is in DC current mode and the cables are in the correct sockets.
Once you have hooked the meter up as above, you can start pulling fuses until the reading drops. This may help you to narrow down the source of the drain.Sorry to go slightly off topic, but what makes you think you have a drain from the battery.
Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
TommyBuoy said:
Sorry to go slightly off topic, but what makes you think you have a drain from the battery.
Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
I think the word you are looking for is current Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
(Been a long time since I did Physics)Would the OP not be better off using a High Rate Discharge Tester, or are these no longer used?
750turbo said:
TommyBuoy said:
Sorry to go slightly off topic, but what makes you think you have a drain from the battery.
Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
I think the word you are looking for is current Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
(Been a long time since I did Physics)Would the OP not be better off using a High Rate Discharge Tester, or are these no longer used?
Edit: Do you have an optimate type charger? What is the interval between charging by driving?
Edited by Smiler. on Wednesday 29th September 12:40
Yeah the stereo is wired in correctly, been in there for 18 months now and I've never had a problem with it. The aftermarket dash control module has only stopped working since the flat battery, so I don't know if that caused the problem in the first place or needs resetting or something.
TommyBuoy said:
Sorry to go slightly off topic, but what makes you think you have a drain from the battery.
Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
The battery itself was tested by a garage yesterday and it's fine apparently. The only aftermarket item is the headunit. To be honest I'm not 100% that it is a drain, but for £12 to check it myself I thought I'd give it a go. Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
To check the alternator is charging okay, with the multimeter you can check the voltage when the engine is running - set the meter to read DC volts, and place the probes across the two battery terminals with the battery leads connected as usual. Depending on the car, a voltage from 13.5 - 16 volts with the engine running means the alternator is charging okay.
To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
Turkey said:
To check the alternator is charging okay, with the multimeter you can check the voltage when the engine is running - set the meter to read DC volts, and place the probes across the two battery terminals with the battery leads connected as usual. Depending on the car, a voltage from 13.5 - 16 volts with the engine running means the alternator is charging okay.
To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
Excellent write up, thank you. I checked the charge in the battery with the engine off and it was at 12.6 (I believe anything between 12.5 - 12.8 is good). With the engine running it was at 14.54 so I am assuming the alternator is healthy.To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
I had a few problems with measuring the drain. I armed the alarm, but when I disconnected the negative lead the alarm went off. Without the alarm set the car was drawing 0.03/0.04 amps. Would having someone set the alarm whilst I held the multimeter between the battery and negative cable work?
Alex97 said:
Turkey said:
To check the alternator is charging okay, with the multimeter you can check the voltage when the engine is running - set the meter to read DC volts, and place the probes across the two battery terminals with the battery leads connected as usual. Depending on the car, a voltage from 13.5 - 16 volts with the engine running means the alternator is charging okay.
To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
Excellent write up, thank you. I checked the charge in the battery with the engine off and it was at 12.6 (I believe anything between 12.5 - 12.8 is good). With the engine running it was at 14.54 so I am assuming the alternator is healthy.To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
I had a few problems with measuring the drain. I armed the alarm, but when I disconnected the negative lead the alarm went off. Without the alarm set the car was drawing 0.03/0.04 amps. Would having someone set the alarm whilst I held the multimeter between the battery and negative cable work?
I think your battery voltage when the car is sat with the engine off could be a bit low. The engine running voltage looks okay though, so the alternator appears to be fine, or at least working quite well. With the voltage at 14.5 volts with the engine running (for a few minutes at least), after switching the engine off, the voltage across a healthy battery should stay at 13 volts or higher for quite some time, as the battery will have a "surface charge" after being charged by the alternator. If not, the battery might be weak.
If the car has been left overnight, then 12.6 volts could be okay though.
On my car, when the battery was dying, the voltage wasn't vety low, it was around 12.6 volts after running the car, switching off, and leaving for an hour or two. But the battery was knackered.
The battery may have a reasonably healthy voltage after being sat for a few hours, but the internals can be worn out, and a lot of plate material could have been damaged or lost over the years.
Given that the alternator is working, and the current drain is normal when the car is idle, I think your battery has given up. If you can, do try getting the alarm to kick in with the multimeter connected to measure the current draw, in case the alarm is draining the power, before buying a new battery.
If the car has been left for weeks/months at all, and the battery has drained, this takes a large chunk out of its lifespan.
Edited by Turkey on Thursday 30th September 22:19
I wrote a small article about failing batteries for my Midget And Sprite Club branch website based on my twenty eight years at the roadside.
It follows the sequence detailed for AA patrol testing in the days before it all became computer driven.
If it's any help it's available here:
http://www.ssnbmasc.byethost32.com/tech.html
It is specifically aimed at Sprite and Midget type technology, but if you have a superdooper modern electronic ignition system (OK, Who doesn't these days) you can simply disconnect the ignition coil to stop the engine starting.
Fer pity's sake don't dis-sconnect the plug leads, you will almost certainly kill the ignition system with stray HT.
You do need a digital multimeter to do the readings.
Be careful, remember what you do is down to you.
Or simply call an AA man with his handy computer which does all this for you.
It follows the sequence detailed for AA patrol testing in the days before it all became computer driven.
If it's any help it's available here:
http://www.ssnbmasc.byethost32.com/tech.html
It is specifically aimed at Sprite and Midget type technology, but if you have a superdooper modern electronic ignition system (OK, Who doesn't these days) you can simply disconnect the ignition coil to stop the engine starting.
Fer pity's sake don't dis-sconnect the plug leads, you will almost certainly kill the ignition system with stray HT.
You do need a digital multimeter to do the readings.
Be careful, remember what you do is down to you.
Or simply call an AA man with his handy computer which does all this for you.
^^ this looks like good info to diagnose a dodgy battery by measuring the voltage drop when cranking. When mine was dying it was getting down to 7 volts when cranking, and showing about 12.5 volts after being sat overnight.
Obviously on a modern car with an ECU/alarm etc. the current draw when the car is sat won't be 0 amps, but just a small current if there are no excessive drains.
Some of the newer maintenance free batteries can have an in-car charging voltage of up to 16 volts or more (on modern Fords especially), and can have a higher standing voltage of up to around 13 volts when fully charged (and surface charge removed).
Obviously on a modern car with an ECU/alarm etc. the current draw when the car is sat won't be 0 amps, but just a small current if there are no excessive drains.
Some of the newer maintenance free batteries can have an in-car charging voltage of up to 16 volts or more (on modern Fords especially), and can have a higher standing voltage of up to around 13 volts when fully charged (and surface charge removed).
Smiler. said:
750turbo said:
TommyBuoy said:
Sorry to go slightly off topic, but what makes you think you have a drain from the battery.
Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
I think the word you are looking for is current Have you checked that enough ampage (is that a word?) is entering the battery when running and how old is the battery?
If you are running anything that is not factory fit then you need to make sure nothing is wired incorrectly or shorting out?
(Been a long time since I did Physics)Would the OP not be better off using a High Rate Discharge Tester, or are these no longer used?
Edited by Smiler. on Wednesday 29th September 12:40
Turkey said:
Alex97 said:
Turkey said:
To check the alternator is charging okay, with the multimeter you can check the voltage when the engine is running - set the meter to read DC volts, and place the probes across the two battery terminals with the battery leads connected as usual. Depending on the car, a voltage from 13.5 - 16 volts with the engine running means the alternator is charging okay.
To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
Excellent write up, thank you. I checked the charge in the battery with the engine off and it was at 12.6 (I believe anything between 12.5 - 12.8 is good). With the engine running it was at 14.54 so I am assuming the alternator is healthy.To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
I had a few problems with measuring the drain. I armed the alarm, but when I disconnected the negative lead the alarm went off. Without the alarm set the car was drawing 0.03/0.04 amps. Would having someone set the alarm whilst I held the multimeter between the battery and negative cable work?
I think your battery voltage when the car is sat with the engine off could be a bit low. The engine running voltage looks okay though, so the alternator appears to be fine, or at least working quite well. With the voltage at 14.5 volts with the engine running (for a few minutes at least), after switching the engine off, the voltage across a healthy battery should stay at 13 volts or higher for quite some time, as the battery will have a "surface charge" after being charged by the alternator. If not, the battery might be weak.
If the car has been left overnight, then 12.6 volts could be okay though.
On my car, when the battery was dying, the voltage wasn't vety low, it was around 12.6 volts after running the car, switching off, and leaving for an hour or two. But the battery was knackered.
The battery may have a reasonably healthy voltage after being sat for a few hours, but the internals can be worn out, and a lot of plate material could have been damaged or lost over the years.
Given that the alternator is working, and the current drain is normal when the car is idle, I think your battery has given up. If you can, do try getting the alarm to kick in with the multimeter connected to measure the current draw, in case the alarm is draining the power, before buying a new battery.
If the car has been left for weeks/months at all, and the battery has drained, this takes a large chunk out of its lifespan.
Edited by Turkey on Thursday 30th September 22:19
Alex97 said:
Turkey said:
Alex97 said:
Turkey said:
To check the alternator is charging okay, with the multimeter you can check the voltage when the engine is running - set the meter to read DC volts, and place the probes across the two battery terminals with the battery leads connected as usual. Depending on the car, a voltage from 13.5 - 16 volts with the engine running means the alternator is charging okay.
To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
Excellent write up, thank you. I checked the charge in the battery with the engine off and it was at 12.6 (I believe anything between 12.5 - 12.8 is good). With the engine running it was at 14.54 so I am assuming the alternator is healthy.To measure the current drain (with the engine off etc.), you need to change the multimeter to measure the DC Amps current draw. Connect the probes to the meter into the correct ports to measure DC amps, on the 10 amp scale (usually). Then set the dial or buttons on the multimeter to go into the DC 10 amps measurement mode.
Then pop the bonnet, and lock the car. If you have a bonnet switch for the alarm, you might need to tape this down to avoid setting the alarm off. After this, disconnect the battery negative lead, and connect one of the multimeter probes to the battery lead, and the other probe to the battery negative terminal, so the multimeter is making the circuit from the battery post the the battery connection lead.
The meter should now give a current reading. It might take a couple of minutes for the current reading to settle down as the cars electrics go into idle modes.
A reading of up to 50 milliamps is probably okay, and shows there is no excessive current drain. 50 milliamps equals 0.05 amps if you have the meter on the 10 amp scale. If it is much higher than this, then you can start pulling fuses to isolate the circuit that is draining the battery. If you have a fusebox inside the car then obviously you can't have the car locked while pulling the fuses.
If the battery voltage reads okay when the engine is running, and the current drain is less than 50 milliamps, I would suspect that the battery is duff, and the diagnostic test done on it was wrong.
I had a few problems with measuring the drain. I armed the alarm, but when I disconnected the negative lead the alarm went off. Without the alarm set the car was drawing 0.03/0.04 amps. Would having someone set the alarm whilst I held the multimeter between the battery and negative cable work?
I think your battery voltage when the car is sat with the engine off could be a bit low. The engine running voltage looks okay though, so the alternator appears to be fine, or at least working quite well. With the voltage at 14.5 volts with the engine running (for a few minutes at least), after switching the engine off, the voltage across a healthy battery should stay at 13 volts or higher for quite some time, as the battery will have a "surface charge" after being charged by the alternator. If not, the battery might be weak.
If the car has been left overnight, then 12.6 volts could be okay though.
On my car, when the battery was dying, the voltage wasn't vety low, it was around 12.6 volts after running the car, switching off, and leaving for an hour or two. But the battery was knackered.
The battery may have a reasonably healthy voltage after being sat for a few hours, but the internals can be worn out, and a lot of plate material could have been damaged or lost over the years.
Given that the alternator is working, and the current drain is normal when the car is idle, I think your battery has given up. If you can, do try getting the alarm to kick in with the multimeter connected to measure the current draw, in case the alarm is draining the power, before buying a new battery.
If the car has been left for weeks/months at all, and the battery has drained, this takes a large chunk out of its lifespan.
Edited by Turkey on Thursday 30th September 22:19
Agree with the above post entirely. Mine draws 0.035 amps (35 milliamps), and when the battery was dying it would appear to start fine in the morning and run fine all day, with the starter cranking quickly. Then then when the weather got a bit colder it would only crank for about 1.5 seconds before the starter motor started clicking away. If the engine started in this time, fine, if it didn't I needed to get it on a small charger for 10 minutes.
The drain is caused by things like the clock, stereo and alarm system, and is normal in a modern car. If the drain was 0.05 amps or more then it would be time to look into a potential circuit problem somewhere, depending on the normal level for the model of car.
Based on the charging voltage and current drain readings you have given I would put money on it being a duff battery.
Quick note to anyone with a Diesel, or fuel burning heater. These cars might run the glow plugs (VW/Audi TDI's?) or heater before the key is put in the ignition, which could fry your multimeter. Best to check first and avoid making these components trigger with the multimeter connected in series.
The drain is caused by things like the clock, stereo and alarm system, and is normal in a modern car. If the drain was 0.05 amps or more then it would be time to look into a potential circuit problem somewhere, depending on the normal level for the model of car.
Based on the charging voltage and current drain readings you have given I would put money on it being a duff battery.
Quick note to anyone with a Diesel, or fuel burning heater. These cars might run the glow plugs (VW/Audi TDI's?) or heater before the key is put in the ignition, which could fry your multimeter. Best to check first and avoid making these components trigger with the multimeter connected in series.
Gassing Station | General Gassing [Archive] | Top of Page | What's New | My Stuff