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I left a 2001 V6 Honda Accord unrun for ~4 months (I don't have a license). Naturally, the battery is dead. I have heard that letting the alternator charge the battery from empty like this puts unnecessary wear on the alternator, so it is best to get a shop charge. Since I don't have a license I can't get it to a shop...

Would it work to fully charge the battery off of a jumper battery (specifically I have access to a jump-n-charge 660, which has 1700 peak amps and 425 cranking amps. http://www.cloreautomotive.com/sku.php?id=244). About how long would it take to charge the engine battery (approximately of course. An hour? 6 hours? 12 hours?). Is there risk of overcharging the engine battery like this?

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    Since no one has mentioned this: Charging a dead battery with the alternator does not put extra wear on the alternator. Focus on your battery's health. It is much more finicky than the alternator.
    – Zach Mierzejewski
    Apr 15, 2016 at 18:25

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Use the jumper battery to start the engine, then disconnect it and leave the engine running (with no current drain such as lights, heater fan, radio, etc). The car should charge its own battery to 80% charge in about two hours (assuming the battery and alternator are in good condition; the battery may be damaged by being uncharged for so long, but I've never had that issue.)

Doing it this way won't damage anything, and if the car is not on a road, you can't be done for being in charge of a car while unlicensed.

Those jump batteries are generally intended for getting the car started; if you want to keep the battery in the car charged, look for a 'trickle charger'.

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Lead acid type batteries, such as this, like to be charged very slowly. Under 5 amps for many hours would be best. During fast charging the internals overheat and electrolyte can boil. Best to charge slowly if time allows.

This type battery has its worst damage happen when it is stored discharged. The chemistry in this state is more acidic. This acid corrodes the plates and does irreparable damage. Best to install a battery maintainer and leave it on all the time the battery is in storage. The maintainer is the difference between 1 year or 4 years of life on my boat battery.

A typical alternator can handle the high rate charge OK most of the time. Heat is the problem here also. But the slow rate charge with a charger is the preferred solution.

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  • Thanks, I bought a small 'car battery charger' about 10 years ago from the local auto parts store, when I was actually looking for a jump starter. Needless to say, it didn't do what I wanted it to, and I deemed it junk. Now I realize it's actually probably a trickle charger, which might work fine for keeping my batteries charged long term. Why I didn't throw it away is a mystery to me, but if it works, I'm glad I didn't :-)
    – MDMoore313
    Apr 15, 2016 at 19:44
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    @BigHomie I got a trickle charger deliberately, but it turned out to be a "Jr" version intended for smaller batteries. I didn't know that you need a bigger trickle charger to charge a bigger battery like a typical 12v car (or in my case pickup truck) battery.
    – stannius
    Apr 15, 2016 at 21:50
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    @stannius You don't. You can use a small one. It will just take a lot longer to actually charge the battery.
    – David Schwartz
    Apr 15, 2016 at 23:10
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A @FredWilson says, you need to charge it slowly - either by driving it around or by using a trickle charger. If you can get a trickle charger with a 'maintenance mode', you can leave it permanently attached to the car and it will keep the battery topped up and stop it going flat in the first place.

If possible, I'd also recommend finding someone you trust and getting them to drive the car around a bit - not only does this help to charge the batter as per @Pete's answer, but it also gets all the fluids moving and keeps the rest of the running gear working.

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