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Car battery to be charged is a DIN66 which I think is about 65ah. I have a Motorcycle charger which says it can be used on cars; it suits batteries from 4 ah to 40 ah.

Does this mean that it can also be used on a bigger battery but it will take longer, or should we just go and get a car charger?

Edit: charger is 12V - 2amp

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Thanks to everyone who answered! I was able to charge the battery with this charger just fine. It was hooked up for about a day before the lights on the charger started to blink and indicate that it was even hooked up (it was dead flat). After that it took about 3 days to reach full charge acording to the the charger. Put it back in and the car started on the first go. –  KiwiNige Oct 6 '11 at 5:37

3 Answers 3

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Basically any source of DC 13-13.8 volts can be used to charge a car battery, and even just 12 volts should get it up enough that you can start the engine and charge the rest of the way from the alternator. I've even used a 12 volt wall-wart before, but it took a while. :-)

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OK, so the charger is 12v - 2 amp, so we can just expect it to take a long time, but that's OK. –  KiwiNige Aug 7 '11 at 8:09
    
@KiwiNige Yes, the amp rating determines the length of time. Lower means longer, so make sure you give it enough time. –  FossilizedCarlos Aug 9 '11 at 12:06
    
A high amp charge could cause problems for a deeply discharged battery so a slow charge should help. My bike charger only charges at 0.5-1amperes as any more could warp the plates in the battery. –  Mauro Dec 2 at 9:05

Yes, you can, but you'll have to be patient. There's nothing inherent in a charger that makes it suitable only for motorcycles or cars, although you'll have to be careful with using a 'car' charger on a motorcycle battery to insure the motorcycle battery doesn't get charged too fast and that the charger used is suitable for the battery type.

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Connecting a lead-acid battery to a dumb charger and leaving it there for a long time is a bad idea.

If your goal is to charge a starter battery to the point where it will start an engine, then the other answers are correct: you can use a smaller charger to get enough energy in there to do the job of starting. Be careful not to overcharge. Once the engine is started, you can let the alternator do its job and charge the rest of the way.

An alternator's regulator controls what voltage comes out, to satisfy the needs of the electrics in the vehicle and to charge the battery. However, when the alternator is turning very slowly, the voltage will be low regardless of the regulator. Thus, in most vehicles the battery won't charge at idle. Hence, the advice to drive at highway speeds to recharge the battery.

Lead-acid batteries like to be charged in a very specific way. They can absorb an enormous amount of energy, very fast, up to around 80% charge, then you have to back off.

From http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery: image

Instead of building a small computer to control charging rates, most regulators take a very simple approach to charging, which means you'll never quite get the maximum charge and maximum life out of a battery. It is possible to install a smart regulator, but at $500 it's not worth it in a car. (It may be worth it for off-grid boats, RVs, and houses.)

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Thanks for this. My charger is also a tender so should be able to be left on without overcharging. And also a switch for Lead Acid and Jell I think. –  KiwiNige Aug 11 '11 at 4:10

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