Are my car batteries dead?
Discussion
just checked both batteries for an e36 and e46 and one is showing 11.6 and the other 11.9 with a voltmeter...ive read that healthy batteries are about 12.4-12.6 nominal voltage?
is it time to replace? no issues with the electrics and all works as it should although the 11.9 one which is in the e46 seems to have a laboured warm start but perhaps not battery related
is it time to replace? no issues with the electrics and all works as it should although the 11.9 one which is in the e46 seems to have a laboured warm start but perhaps not battery related
A fully charged healthy battery should show 12.6 volts.
Anything below 12.4 volts is potential trouble.
Anything under 12.1 volts is knackered.
To get the voltage readings properly,
Anything below 12.4 volts is potential trouble.
Anything under 12.1 volts is knackered.
To get the voltage readings properly,
- Remove battery from car
- Charge the battery fully
- Bring the battery indoors and let it stand overnight (to stabilise after charging and to get it to room temperature)
- Measure the voltage in the morning.
OP, you need to check the voltage across the terminals when the engine is running 
- you'd ideally be looking at 14.0v to 14.8v (higher is better)... The battery will show a lower voltage when left standing, admittedly - 12.3v isn't uncommon for a reliable battery, for example 
.
One realistic test is to get in the car, keeping the key away from the ignition, and switch dipped beam on and see how long the headlights remain brightly lit... Figures on the back of a fag packet indicate that for every hour the headlights remain bright there's at the very least 12A/h in the battery - and 18A/h (that's the equivalent of 90 minutes with the headlights on and the car parked up before they fade out cue a battery recharge) will start up a petrol 309 1600 without any difficulty on the coldest day you'll generally experience in Bolton (where I am located on the northern fringe up in t'hills) .
You'll have to recharge the battery (24 hours as a minimum as a guideline) after the headlights have browned out, admittedly , and the battery might need topping up with deionised water as a routine maintenance jobbie as well.
Bleak "the voltage is x therefore it's fecked" statements don't tell the whole tale in isolation !
- you'd ideally be looking at 14.0v to 14.8v (higher is better)... The battery will show a lower voltage when left standing, admittedly - 12.3v isn't uncommon for a reliable battery, for example .One realistic test is to get in the car, keeping the key away from the ignition, and switch dipped beam on and see how long the headlights remain brightly lit... Figures on the back of a fag packet indicate that for every hour the headlights remain bright there's at the very least 12A/h in the battery - and 18A/h (that's the equivalent of 90 minutes with the headlights on and the car parked up before they fade out cue a battery recharge) will start up a petrol 309 1600 without any difficulty on the coldest day you'll generally experience in Bolton (where I am located on the northern fringe up in t'hills)
.You'll have to recharge the battery (24 hours as a minimum as a guideline) after the headlights have browned out, admittedly
, and the battery might need topping up with deionised water as a routine maintenance jobbie as well.Bleak "the voltage is x therefore it's fecked" statements don't tell the whole tale in isolation
!When the engine's running all you'll ever see is the voltage off the alternator.
The voltage on a lead acid battery that's been charged and left to stand for a few hours DOES tell you a lot about its condition, exactly as per my post above.
The best way of all to get a battery tested is to go to a battery specialist and get them to do a high drain test on it. Take your wallet with you...
The voltage on a lead acid battery that's been charged and left to stand for a few hours DOES tell you a lot about its condition, exactly as per my post above.
The best way of all to get a battery tested is to go to a battery specialist and get them to do a high drain test on it. Take your wallet with you...
I've found very little difference in the voltage of a worn out maintenance free (sealed type, calcium technology) battery and one that is healthy - both dropped to around 13.2-13.6 volts almost straight after turning the engine off, and would read about about 12.6-12.7 volts after being left overnight (approx. 12-18 hours) after driving. Are you sure the voltmeter is reading okay though as those voltages do both sound low to allow enough power for good cold starting.
A load test would reveal all, but I suspect your multimeter is off, as with both batteries showing less than 12V I would expect some signs of weakness on a cold start, which puts more strain on the battery than a warm one.
A load test would reveal all as mentioned above, but if both cars are starting okay I would assume the multimeter might be under reading, and even if not, voltage isn't a great indicator of battery life remaining, only state of charge. For example, a battery with only 25% of it's meat left for storing energy, will show a similar voltage to a brand new one when fully charged, it's just that there's only 25% of the battery plates left intact and able to store charge, so unless left with the alarm and accessories draining for a long time and zapping that available energy stored, a brand new battery could give the same voltage as a worn out one, but have much less energy available to deliver to start the car.
A load test would reveal all, but I suspect your multimeter is off, as with both batteries showing less than 12V I would expect some signs of weakness on a cold start, which puts more strain on the battery than a warm one.
A load test would reveal all as mentioned above, but if both cars are starting okay I would assume the multimeter might be under reading, and even if not, voltage isn't a great indicator of battery life remaining, only state of charge. For example, a battery with only 25% of it's meat left for storing energy, will show a similar voltage to a brand new one when fully charged, it's just that there's only 25% of the battery plates left intact and able to store charge, so unless left with the alarm and accessories draining for a long time and zapping that available energy stored, a brand new battery could give the same voltage as a worn out one, but have much less energy available to deliver to start the car.
Edited by Turkey on Tuesday 15th April 21:38
http://www.meeknet.co.uk/e38/E38_Battery_SOC_Table...
According to the data in the link above the two most common car battery types should both be dead at 11.8 volts (no charge left)so I would definitely check your multimeter. This is general data so I wouldn't rely on it as being gospel as there will be some voltage difference between different variations on those types of batteries, but not much more than 0.1-0.2 volts I don't think.
According to the data in the link above the two most common car battery types should both be dead at 11.8 volts (no charge left)so I would definitely check your multimeter. This is general data so I wouldn't rely on it as being gospel as there will be some voltage difference between different variations on those types of batteries, but not much more than 0.1-0.2 volts I don't think.
aw51 121565 said:
OP, you need to check the voltage across the terminals when the engine is running - you'd ideally be looking at 14.0v to 14.8v (higher is better)... The battery will show a lower voltage when left standing, admittedly - 12.3v isn't uncommon for a reliable battery, for example .
I'd be concerned there was an issue with the alternator if it was charging at 14.8v's tbh, anything over 14.5 isn't 'normal'. - you'd ideally be looking at 14.0v to 14.8v (higher is better)... The battery will show a lower voltage when left standing, admittedly - 12.3v isn't uncommon for a reliable battery, for example .As others have said, checking the voltage with the car running is pointless if you want to check the battery condition. Either faff about taking it off and charging it or get it tested by a battery load tester after a 20 minute run
TBH, if the cars start fine everytime you go to use them there is no point testing the voltage anyway
Jimmyarm said:
I'd be concerned there was an issue with the alternator if it was charging at 14.8v's tbh, anything over 14.5 isn't 'normal'.
As others have said, checking the voltage with the car running is pointless if you want to check the battery condition. Either faff about taking it off and charging it or get it tested by a battery load tester after a 20 minute run
Depends on the charging system. Some put upto 18v in straight straight start up.As others have said, checking the voltage with the car running is pointless if you want to check the battery condition. Either faff about taking it off and charging it or get it tested by a battery load tester after a 20 minute run
Jimmyarm said:
TBH, if the cars start fine everytime you go to use them there is no point testing the voltage anyway
That certainly used to be true.But with modern car computery you can get into difficulties with a weak battery which is still perfectly capable of cranking the engine,
- Starter motor - needs high current and doesn't care much about voltage
- Computer - needs correct voltage and doesn't draw much current
Car electrics are a mysterious thing.
Ozzie Osmond said:
Jimmyarm said:
TBH, if the cars start fine everytime you go to use them there is no point testing the voltage anyway
That certainly used to be true.But with modern car computery you can get into difficulties with a weak battery which is still perfectly capable of cranking the engine,
- Starter motor - needs high current and doesn't care much about voltage
- Computer - needs correct voltage and doesn't draw much current
Car electrics are a mysterious thing.
Modern cars with dodgy batteries do very odd things.
My Audi used to give brake pad warnings and wiper fluid warnings for no reason until I got it checked - and it was a duff battery.
Changed for free by Audi as it was quite new at the time.
Ozzie Osmond said:
Jimmyarm said:
TBH, if the cars start fine everytime you go to use them there is no point testing the voltage anyway
That certainly used to be true.But with modern car computery you can get into difficulties with a weak battery which is still perfectly capable of cranking the engine,
- Starter motor - needs high current and doesn't care much about voltage
- Computer - needs correct voltage and doesn't draw much current
Agreed, our Focus, started perfectly. Stopped at shop. Wouldn't restart. Got a bump down the hill still wouldn't start and made some odd noises. Just on way to airport so was very concerned. AA man said knackered battery, wasn't convinced. 6 months later hasn't missed a beat. Not the cheapest battery but is covered for 4 years even if you don't renew membership.
Old seemingly shagged batteries can be revived with gentle charging. Buy an 'Optimate' i have quite a few allegedly dead batteries in the garage revived after use, (replaced at the time), does take around a week to revive them though so no good in emergencies. Has been used on car / motorbike / lawnmower / UPS batteries with great success. Best £40 i've spent in a while.
Car electrics are a mysterious thing.
Leptons said:
Depends on the charging system. Some put upto 18v in straight straight start up.
Which every day car puts 18v out of the alternator on start up ?As for a weak battery messing with the ECU's etc, yes this can happen but it is usually pretty obvious (eta to someone that knows what they are looking at when diagnosing). As I said, if it starts and runs fine then there are no issues to worry about for the moment with slightly low voltages on the OP's batteries.
Jimmyarm said:
As for a weak battery messing with the ECU's etc, yes this can happen but it is usually pretty obvious (eta to someone that knows what they are looking at when diagnosing). As I said, if it starts and runs fine then there are no issues to worry about for the moment with slightly low voltages on the OP's batteries.
It does odd things. My shed which has hydraulic power steering didn't work for a while after having a bump start. ABS / ESP / AirBags all showed errors until it had been run for a while.There are so many linked systems that need to boot up before a modern car works fully.
Thank fook Apple don't supply the OS for them, we'd all be waiting for iToons to synch before heading off to work.
The_Burg said:
It does odd things. My shed which has hydraulic power steering didn't work for a while after having a bump start. ABS / ESP / AirBags all showed errors until it had been run for a while.
There are so many linked systems that need to boot up before a modern car works fully.
Thank fook Apple don't supply the OS for them, we'd all be waiting for iToons to synch before heading off to work.
All modern car's do odd things if you mess with their normal operation, bump starting something is just that.There are so many linked systems that need to boot up before a modern car works fully.
Thank fook Apple don't supply the OS for them, we'd all be waiting for iToons to synch before heading off to work.
Newer Clio's with electric steering are a pita, you start it and go to turn the wheel and there is no assistance for 2 or 3 seconds whilst it starts up (the car doesn't supply power to the steering motor until it has started as it wouldn't work under the cranking load from the start motor).
As I have said a couple of times, if it starts and runs fine, there is nothing wrong !
Jimmyarm said:
The_Burg said:
It does odd things. My shed which has hydraulic power steering didn't work for a while after having a bump start. ABS / ESP / AirBags all showed errors until it had been run for a while.
There are so many linked systems that need to boot up before a modern car works fully.
Thank fook Apple don't supply the OS for them, we'd all be waiting for iToons to synch before heading off to work.
All modern car's do odd things if you mess with their normal operation, bump starting something is just that.There are so many linked systems that need to boot up before a modern car works fully.
Thank fook Apple don't supply the OS for them, we'd all be waiting for iToons to synch before heading off to work.
Newer Clio's with electric steering are a pita, you start it and go to turn the wheel and there is no assistance for 2 or 3 seconds whilst it starts up (the car doesn't supply power to the steering motor until it has started as it wouldn't work under the cranking load from the start motor).
As I have said a couple of times, if it starts and runs fine, there is nothing wrong !
OP, I have had a flat battery that has intermittently been unable to start the car recently. I've checked my voltages and seem to be in a similar scenario to you, albeit slightly further down the road (02 E46 330ci on original battery).
Read volts after a 20 minute drive (11.6).
Whilst running (14.something, can't quite remember but shows alternator was working.
This week I pulled the fuse on my final stage resistor to ensure that wasn't going faulty and running when my ignition/car was off. For me, this didn't have any affect on keeping the battery alive, after a 20 minute run, I went for a 1 mile drive and after this it died.
May not be exactly the same as you're experience but I've gone and bought a new Exide Premium battery from CP4L ~£75 and am hoping this issue will be sorted.
Read volts after a 20 minute drive (11.6).
Whilst running (14.something, can't quite remember but shows alternator was working.
This week I pulled the fuse on my final stage resistor to ensure that wasn't going faulty and running when my ignition/car was off. For me, this didn't have any affect on keeping the battery alive, after a 20 minute run, I went for a 1 mile drive and after this it died.
May not be exactly the same as you're experience but I've gone and bought a new Exide Premium battery from CP4L ~£75 and am hoping this issue will be sorted.
So those massive '2 prongs' gizmos motor factors use to 'always tell you your battery is knackered' are snake-oil then or what??
I assume they put a load over the battery and check to see if it continues to deliver current - if the current falls-off too quickly, the battery is snorkelled?
All this 'remove it and put it in the house and stroke it and introduce it to your kids' stuff sounds complicated ;0
I assume they put a load over the battery and check to see if it continues to deliver current - if the current falls-off too quickly, the battery is snorkelled?
All this 'remove it and put it in the house and stroke it and introduce it to your kids' stuff sounds complicated ;0
405dogvan said:
So those massive '2 prongs' gizmos motor factors use to 'always tell you your battery is knackered' are snake-oil then or what??
I assume they put a load over the battery and check to see if it continues to deliver current - if the current falls-off too quickly, the battery is snorkelled?
That's right. High drain test is the only real way to check a battery. As you suggest, when "garage bloke" says to "average punter" your battery's snorkelled it's hard to resist the sale. How long's a piece of string?!I assume they put a load over the battery and check to see if it continues to deliver current - if the current falls-off too quickly, the battery is snorkelled?
405dogvan said:
All this 'remove it and put it in the house and stroke it and introduce it to your kids' stuff sounds complicated ;0
Totally agree. However, in the absence of a proper battery tester it's the best DIY alternative.Batteries look simple but they are tricky things and can fail in many different ways and show many different symptoms.
The key thing with a car battery is that it's NOTHING like a mobile phone battery.
- Mobile phone battery is happy to be flattened/recharged/flattened/recharged.
- Car battery HATES being flattened. It's designed to be kept fully charged ALL the time. It doesn't run the car - your alternator does that - all the battery does is start the car. What it likes best is rapid top-up by the alternator after every start and then to sit quietly minding its own business. If your car has a voltmeter you can watch this happening,#
- Ignition on - about 12.5v
- Starter motor - voltage will drop momentarily
- Engine first running - you may well see something up to 15v
- After driving for 15 minutes - voltage will probably be down in the low/mid 14s.
Jimmyarm said:
Which every day car puts 18v out of the alternator on start up ?
As for a weak battery messing with the ECU's etc, yes this can happen but it is usually pretty obvious (eta to someone that knows what they are looking at when diagnosing). As I said, if it starts and runs fine then there are no issues to worry about for the moment with slightly low voltages on the OP's batteries.
Fords smart charge system.As for a weak battery messing with the ECU's etc, yes this can happen but it is usually pretty obvious (eta to someone that knows what they are looking at when diagnosing). As I said, if it starts and runs fine then there are no issues to worry about for the moment with slightly low voltages on the OP's batteries.
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