Information from a car battery with multimeter?
Discussion
Just want to get an idea of the condition of the battery in my car, it appears that it's 6 years old judging by the service history, but the car seems to start find and is in pretty much daily use and most of my trips are 30-40mins each.
I did a quick check of the charging voltage which was around 13.95V, but what's the best way to check it when it's off? I'm guessing it's best to wait after a drive to let all the electrics shut down etc, and some have said to turn the full beams on for 15secs and then wait a while....Would it be worthwhile checking the voltage after doing that, and then checking again the following morning to see if the voltage has dropped much?
I know it seems like a pointless exercise, but with winter coming up I don't really fancy my car not starting. Being 6 years old, it may be due for a change anyway....
Many thanks.
I did a quick check of the charging voltage which was around 13.95V, but what's the best way to check it when it's off? I'm guessing it's best to wait after a drive to let all the electrics shut down etc, and some have said to turn the full beams on for 15secs and then wait a while....Would it be worthwhile checking the voltage after doing that, and then checking again the following morning to see if the voltage has dropped much?
I know it seems like a pointless exercise, but with winter coming up I don't really fancy my car not starting. Being 6 years old, it may be due for a change anyway....
Many thanks.
The rapidfit places have a test device that puts a starter type load on the battery and measures the voltage. You can take it there or you can DIY with a multimeter.
Your alternator is putting out 13.3-14V running so that's good.
Turn it off, then switch on the lights, wet the screen, wipers, heated screen, leave it all on for say 2 minutes. Measure the voltage at the battery. Anything under 12, or certainly 11.5 in this time is bad news. Worst news is any rapid falls in voltage while the load is on.
Turn it all off, within a minute the battery should come back to 13 or 13.5.
With the multitester across the battery so you can see it (or get an assistant), hit the starter. Ideally disable the engine so it won't start so that you can have a good crank. It should maintain over 9V when cranking. If not, dead.
Batteries are funny things. These days with modern ECUs and heavy electrical loads but first time every time starting you get little warning of them going down. The days of limping a tired Cortina battery around for weeks, charging it every weekend, are gone. They can be fine until one day they just fall over.
One thing that I've had is a "final straw" event that just tips an apparently good battery over the edge. Usually it's a daytime stop somewhere in poor viz, so lights on. You spend an hour in a service station and forget to turn them off. An hour later it's dead, or near dead. You get a jump or a push, on you go. After that it's curtains, the thing refuses to start 2 days later. I don't recommend it but you could try this. Leave the lights on for an hour, if it tolerates this it's definitely good. If not then you probably had it coming anyway so replace it.
Your alternator is putting out 13.3-14V running so that's good.
Turn it off, then switch on the lights, wet the screen, wipers, heated screen, leave it all on for say 2 minutes. Measure the voltage at the battery. Anything under 12, or certainly 11.5 in this time is bad news. Worst news is any rapid falls in voltage while the load is on.
Turn it all off, within a minute the battery should come back to 13 or 13.5.
With the multitester across the battery so you can see it (or get an assistant), hit the starter. Ideally disable the engine so it won't start so that you can have a good crank. It should maintain over 9V when cranking. If not, dead.
Batteries are funny things. These days with modern ECUs and heavy electrical loads but first time every time starting you get little warning of them going down. The days of limping a tired Cortina battery around for weeks, charging it every weekend, are gone. They can be fine until one day they just fall over.
One thing that I've had is a "final straw" event that just tips an apparently good battery over the edge. Usually it's a daytime stop somewhere in poor viz, so lights on. You spend an hour in a service station and forget to turn them off. An hour later it's dead, or near dead. You get a jump or a push, on you go. After that it's curtains, the thing refuses to start 2 days later. I don't recommend it but you could try this. Leave the lights on for an hour, if it tolerates this it's definitely good. If not then you probably had it coming anyway so replace it.
Amazing what symptoms a dead battery will show.
I was working at a place where the ground workers had a fairly new vw crafter. When the battery died the ecu went mental, indicators flashing, parking light wouldn't switch off, gearbox warnings all sorts.
I thought the guys were going to be getting a massive bill for that lot, RAC turned up sorted the battery and off they went.
I was working at a place where the ground workers had a fairly new vw crafter. When the battery died the ecu went mental, indicators flashing, parking light wouldn't switch off, gearbox warnings all sorts.
I thought the guys were going to be getting a massive bill for that lot, RAC turned up sorted the battery and off they went.
That' the most reliable test and it takes 2 minutes. Watch them doing it, it's good fun. The device is just 2 prongs with insulated handles, a voltmeter and a bloody great resistor coil between the two prongs. God knows what current it pulls, it's several tens of amps, possibly 100. The test is to monitor the battery under heavy load and see how well it stands up.
Let me guess what your mate will say:
"Yeah, it's OK. It's a bit under, but still OK. Up to you, no rush, it might go through the winter or fail next week. It's hard to tell."
You'll then buy a new battery. At the end of the day a biggish battery comes in at £50-60. That's not a tank of fuel, if the existing one is 6 yrs old it won't last for ever, and £60 means that you will no longer worry about it.
Let me guess what your mate will say:
"Yeah, it's OK. It's a bit under, but still OK. Up to you, no rush, it might go through the winter or fail next week. It's hard to tell."
You'll then buy a new battery. At the end of the day a biggish battery comes in at £50-60. That's not a tank of fuel, if the existing one is 6 yrs old it won't last for ever, and £60 means that you will no longer worry about it.
battered said:
That' the most reliable test and it takes 2 minutes. Watch them doing it, it's good fun. The device is just 2 prongs with insulated handles, a voltmeter and a bloody great resistor coil between the two prongs. God knows what current it pulls, it's several tens of amps, possibly 100. The test is to monitor the battery under heavy load and see how well it stands up.
Stand well back, I know someone who did that test but made the mistake of doing it with the filling plugs out, spark jumped off the terminal and into the battery, the explosion hit him full in the face resulting in the loss of sight in one eye!Made me treat big battery's with great respect.
Easternlight said:
battered said:
That' the most reliable test and it takes 2 minutes. Watch them doing it, it's good fun. The device is just 2 prongs with insulated handles, a voltmeter and a bloody great resistor coil between the two prongs. God knows what current it pulls, it's several tens of amps, possibly 100. The test is to monitor the battery under heavy load and see how well it stands up.
Stand well back, I know someone who did that test but made the mistake of doing it with the filling plugs out, spark jumped off the terminal and into the battery, the explosion hit him full in the face resulting in the loss of sight in one eye!Made me treat big battery's with great respect.
They did a battery test and said it's fine and not to bother replacing it yet 
Happy days. I did notice in the service history that it was replaced after 5 years and 25k miles.....5 years later it's on 85k miles, so mileage has really gone up, so the car is getting more use (likely longer trips) and therefore it should last longer.
Cheers for your help chaps.
Is there any point in hooking it up to a charger (I've got a CTEK MXS 5.0) once every month or so for 24 hours? Or, if the alternator is working fine, is that pointless?
Cheers
Happy days. I did notice in the service history that it was replaced after 5 years and 25k miles.....5 years later it's on 85k miles, so mileage has really gone up, so the car is getting more use (likely longer trips) and therefore it should last longer.
Cheers for your help chaps.
Is there any point in hooking it up to a charger (I've got a CTEK MXS 5.0) once every month or so for 24 hours? Or, if the alternator is working fine, is that pointless?
Cheers
E65Ross said:
They did a battery test and said it's fine and not to bother replacing it yet
Blimey, that's a surprise. Result.[quote]
Is there any point in hooking it up to a charger (I've got a CTEK MXS 5.0) once every month or so for 24 hours? Or, if the alternator is working fine, is that pointless?
Chargers are pointless unless cars sit unused, are constantly abused on very short trips, or are antiques with dynamos.
battered said:
E65Ross said:
They did a battery test and said it's fine and not to bother replacing it yet
Blimey, that's a surprise. Result.E65Ross said:
Is there any point in hooking it up to a charger (I've got a CTEK MXS 5.0) once every month or so for 24 hours? Or, if the alternator is working fine, is that pointless?
Don't waste your time or your money. The battery gets hooked up to the best charger in the world twice a day in the week, so it doesn't need any more.Chargers are pointless unless cars sit unused, are constantly abused on very short trips, or are antiques with dynamos.
I was a bit annoyed by the battery on my Civic, because it died about 7 week shy of the cars 13th birthday. It had been getting lazy to start for several months before.
On the testing front, surely if the cars starts all is well. You can normally tell when the battery is getting weak long before it fails.
On the testing front, surely if the cars starts all is well. You can normally tell when the battery is getting weak long before it fails.
battered said:
Willy Nilly said:
You can normally tell when the battery is getting weak long before it fails.
Not IME. One minute they are fine, the next there's a groan when you hit the starter and that's the end of it. Cue it not starting tomorrow morning
At least with batteries I can either order online and get next day delivery FOC, or my AA membership can tow me to my mates garage up the road and they can get it done there for me.
I've replaced the batteries in 4 cars over the past 5 years:
MX5 NC - a bit slow cranking
BMW E61 - kept going into power saving mode overnight
Mini Cooper S - just died, wouldn't crank, but loads of warning lights
Porsche 911 964 - totally dead after sat for a few days
So, 2 gave warning signs, 2 didn't.
MX5 NC - a bit slow cranking
BMW E61 - kept going into power saving mode overnight
Mini Cooper S - just died, wouldn't crank, but loads of warning lights
Porsche 911 964 - totally dead after sat for a few days
So, 2 gave warning signs, 2 didn't.
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