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Testing car batteries?


Aragorn
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I've ended up with a collection of standard car batteries in my garage from various cars i've dismantled over the past couple of years. Theres probably 5 or 6 there. I'm having a good clear out and want to get rid of any that are duff.

I know some of them are (or at least were) in good working order, and others were at least suspect at time of removal.

Is there any decent/reliably/easy way of testing them out? I could probably pick out a couple that i knew were suspect and that i wouldn't trust, but I'd like to test them all to give me a good idea of their condition. After all even the "working" ones could well be in a degraded state with not much life left in them, and thus theres no point keeping them as a spares!

I'm thinking if i could apply some sort of load to them, perhaps a couple of headlamp bulbs or similar, for some period of time and measure how discharged they become after that time, i could at least have some idea of what condition they are in.

I know you can buy specific battery testers, but they seem a lot of money for a one off like this!

Any thoughts?

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I think you need to have them tested, probably what is meant by the 'drop test' that's been suggested. Bearing in mind that voltage output on it's own is useless, as a battery giving out 12 volts can be incapable of even turning an engine over, it's the amps that count & checking that that needs hefty equipment.

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I favour the 'coat hanger test', but it won't win any health and safety awards!

Having given the batteries a good charge, use a wire coat hanger to short between the battery terminals.

By looking at how quickly the wire glows red hot you will get a feel for the condition of the battery.

Obviously don't hold on to the wire between the terminals as that will really ruin your day. Don't hold it on there too long either - the wire will break up and disappear through the top of the battery.

Coat hanger is a little too thin actually; ideally you want something a little thicker.

I will now wait for everyone to tell me this is a stupid thing to do. :glare:

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haha i think i'll pass on the coat hanger!

as Landy Novice suggested i stuck each of them on my (semi) smart charger this morning. Two of them came up "Fault" and wouldnt charge at all so that ruled them out pretty quickly, the others appeared to be full, they started charging then the charger dropped out to its trickle mode within a few minutes and the "full" indicator came on. I guess the fact that they're full is a good thing, in that they've not drained themselves having been stood there for some months, but one of those was definitely suspect.

Will see if i can find somewhere local that can drop test them, or alternatively, see if i can buy/borrow a tester.

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Are they al sealed type or can you see the acid levels inside? Are the casings bloated out as if the plates are heavily sulphated?

The smart charger showing fault may be just saying 'this battery is taking too much voltage, I'll trip out' Maybe try this one on a simple dumb charger for a few hours to get a few not so smart volts into it, then pop it back on the smart charger. If the plates are heavily sulphated and it's gassed all of its acid out then the scrappy will give you a tenner for it

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Wire coat hangar - what a stupid thing to suggest to anybody that might not know better.

A simple, foolproof method of testing a lead/acid battery is with a Battery Hydrometer http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_530647_langId_-1_categoryId_255205

Votmeter reading - ON LOAD will give an indication, but not very reliable.

Cheers,

Tony

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Wire coat hangar - what a stupid thing to suggest to anybody that might not know better.

The method is not the most sensible I grant you, but I think it is up to the individual to asses whether it is suitable (as he did), rather than pre-emptively censoring it. I did add the necessary warnings.

A hydrometer gives a good indication of state of charge for a good battery, but I'm not sure how accurate it would be with a battery that has previously suffered sulfation. I have certainly had batteries where the 'magic eye' indicates fully charged, but where the the internal resistance is such that it will not start a vehicle.

Votmeter reading - ON LOAD will give an indication, but not very reliable.

Voltage under load is the most accurate measurement, since it is voltage under load that starts your engine. Specific gravity of the electrolyte is just an inference.

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A simple, foolproof method of testing a lead/acid battery is with a Battery Hydrometer http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_530647_langId_-1_categoryId_255205

unless there a sealed battery which renders it 100% useless... :blink:

either way, coat hanger or my idea, they still have to be left for a while to give it a chance to discharge (if its duff) no point taking it off charge and testing it straight away..

and on the other hands, the scrape value of lead these day is just gorgeous. so personally, i would be looking to scrap as many as poss. :rofl:

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The method is not the most sensible I grant you, but I think it is up to the individual to asses whether it is suitable (as he did), rather than pre-emptively censoring it. I did add the necessary warnings.

A hydrometer gives a good indication of state of charge for a good battery, but I'm not sure how accurate it would be with a battery that has previously suffered sulfation. I have certainly had batteries where the 'magic eye' indicates fully charged, but where the the internal resistance is such that it will not start a vehicle.

Voltage under load is the most accurate measurement, since it is voltage under load that starts your engine. Specific gravity of the electrolyte is just an inference.

Now you seek to justify such an idea.

I give up!

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and on the other hands, the scrape value of lead these day is just gorgeous. so personally, i would be looking to scrap as many as poss. :rofl:

Thats my thinking ;)

However, I would like to keep at least one spare, as its useful to have a fully charged battery knocking around for various tasks. I also have two projects that will need batteries, so if there are three decent serviceable units then it makes sense to keep them, rather than scrap them all and need to shell out £££ for new batteries in a few months time when i need them!

Out of the four that charged ok, i believe three came from running cars, and thus should be at least half way decent. The last one i'm most dubious about, I'm fairly sure it charged up ok, but couldnt actually start the car, so i think i will just scrap the iffy one with the others.

The remaining three i'll try and get properly tested. I see the kwikfit at the bottom of the road offers a free battery test, so maybe i'll give them a go and see what they say.

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On a slant to this post - if there's one thing I've learnt ove the years is that it's a waste of money buying expensive batteries if you just want a standard unit (as opposed to extra power for winches etc.) The so called extended warranty batteries rarely justify their inflated price tag in terms of service life, my current bog standard item has been on the RRC V8 for just over three years & continues to spin the engine over as fast as ever, despite the car being parked in a exposed location & only being used for 20-40 miles once a week/ten days.

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On a slant to this post - if there's one thing I've learnt ove the years is that it's a waste of money buying expensive batteries if you just want a standard unit (as opposed to extra power for winches etc.)

Not necessarily true: on a lot of vehicles manufactured this century getting the right battery is rather important - the alternator's charge output is matched to the correct battery's characteristics and is computer-controlled; get this wrong and you can easily have a slew of obscure error-codes being logged on various systems because the [wrong] battery doesn't respond in the expected way to accelerated charging.

"Smart charge" is now standard on most European Ford/Volvo/Mercedes/Audi/GM products - the battery needs to be able to handle an alternator output of up to 17 volts after a cold-start.

For the last decade I've always had a preference for Varta, Bosch or Yuasa batteries - they generally come with a five-year warranty which I've so far not needed to take up. To me, a good battery is a cheap investment - I'd rather pay £120 for a decent one than go for a £80 no-name-special which after a couple of years leaves me stranded somewhere spectacularly-inconvenient at 02:00 with a non-starting vehicle when I really need to be 300 miles away.

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Discovery 3 also uses up to 17v to charge the battery and I would assume later models do as well but I'm out of that now.

The old LR genuine batteries (Delphi made I think) are the best I've come across - my Discovery V8 is still on its original battery and is 11 years old in April. It wouldn't start a diesel now, and it will go flat if the vehicle is left more than a couple of weeks, but I don't think it owes me anything!

Having sold batteries for quite a few years, I can tell quite a lot about a battery condition just from the voltage, but you need to know how your own voltmeter reads from experience. DVMs might show voltage to 0.01v but they are not that accurate and a couple of percent error (2% = 0.24v) is the same as the difference between a good and indifferent battery, so you need to know how the meter behaves. You really want a hydrometer and a drop tester to do it properly but I'd guess I can make a fairly accurate assessment on a battery about 95% of the time with just a multimeter.

The "smart" chargers are not all they are cracked up to be IMO, I got one because loads of people rave about them, but it often says a battery is charged when I know it isn't, it gets a sulk when you put it on a battery that is very flat and has condemned a couple that just needed a good charge to recover, and overall it does a less convincing job of charging them than my old Maypole 6a auto charger which was about £15. The good thing is that you can put them on and leave them indefinitely.

Old batteries are often useful to have around - even if they are not perfect they can give enough boost to a battery that is just too flat to start a vehicle, and come in handy for other things. I've had one for about five years that came out of a vehicle it wouldn't start in winter, but it will happily run a 12V drum pump that sucks 15 amps for half an hour.

I've, er, never used a coat hanger. I'll leave it at that!

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I hate these modern ECU controlled vehicle charging systems. The MINI has killed the charging board on two jumpstart boxes now. The main reason for using the box is to power a vhf/uhf ham radio (isolating it from the car) and it's handy for assisting the Morgan to start if it's not been used for a while (i.e. priming mechanical fuel pump!).
I'm wondering whether to return the second Jumstart box for a refund, or whether to try to find an alternative... Meanwhile the old CTEK charger is handy for topping it up each week.

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Not necessarily true: on a lot of vehicles manufactured this century getting the right battery is rather important - the alternator's charge output is matched to the correct battery's characteristics and is computer-controlled; get this wrong and you can easily have a slew of obscure error-codes being logged on various systems because the [wrong] battery doesn't respond in the expected way to accelerated charging.

I don't think we are singing from the same hymm-sheet here. I make sure that the battery in question is the correct one for the car of course, it's just that I only go for the basic model price range, in this case £75 & two year 'no quibble' warranty from my local auto-shop. My '87 RRC has never heard of things like error codes anyway, I'm a great believer in the saying 'if it's fitted then sooner or later it will go wrong'

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