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Suppose a car owner lives in an apartment building and parks his car nearby. He wants to detach the battery, bring it home and charge it with a mains-powered charger indoors.

How to properly handle the battery so that no damage is done to people and property?

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Precaution number 1: Don't do it inside your home! If you "have to" keep it in an isolated room with a fire alarm, and the windows ajar for good ventilation in case of any vapours. But dont make a habit of it. – ppumkin Feb 10 '12 at 9:10
Why? Is the battery dead and he wants to charge it 1 time? Or does he leave his car idle for months at a time and he wants to keep the battery topped off? – Jay Bazuzi Feb 15 '12 at 17:54
@Jay Bazuzi: In this scenario the battery is suddenly dead because of very cold weather and the car being driven for not enough miles to recharge it. – sharptooth Feb 16 '12 at 7:03

2 Answers

up vote 3 down vote accepted

Caveat: I wouldn't charge a battery indoors.

A battery represents a heavy mass of chemical and electrical energy. It should be treated as a fairly dangerous object if it makes its way into your home. Some of the risk factors include:

Heavy: a car battery is a heavy object. Ensure that it is in a stable location with no change of tipping or falling because it is full of ...

Acid: a car battery is full of sulphuric acid. Ensure that is has no chance of tipping, spilling or otherwise expelling acid onto people, pets, valuables or even many metals. Remember, you are about to make the situation even worse by introducing ...

Electricity: be very careful with the terminals of a car battery. There are plenty of amps in there waiting to jump into a conductor and make enormously exciting and dangerous sparks. Keep in mind that when charging a car battery, it will produce hydrogen gas of some concentration. Ensure that the environment is well ventilated because otherwise there's an excellent chance of a dangerous ...

Fire: have a fire extinguisher in your hand. Note: you will have to make a judgment call on what type you need: what will the hydrogen ignite and how will you put it out? Where will the acid go when you start hosing it around with the extinguisher?

If I were forced to do this inside my house, I would put the battery in a large Pyrex casserole dish on the floor, run the charger from a GFCI outlet (to act as an additional ciruit breaker) and keep the fire extinguisher in my hand.

I would also wait until my wife was not home and I would not tell her later about the dumb thing I did today....

In all seriousness, what I would do (and have done) is to connect the battery charger to the battery while it's still in the car. Then I would plug the charger into an extension cord (or series thereof) until such time as I could reach a plug with main power. The risks of a car battery inside the house are significant and the benefits (convenience? hardly!) are small enough that they're difficult to measure.

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There are so many reasons not to charge a car's starter battery in a living space:

  • battery acid on your clothes when you carry it

  • hydrogen buildup that could explode

  • you're going to use an all-metal wrench to remove the battery cables, which makes it easily to accidentally create a short circuit on a device designed to dump a lot of amps quickly

The easiest way to deal with this problem is to jump-start the car and then drive to recharge the battery. You don't have to remove the battery, or risk hydrogen buildup indoors, or get battery acid on your clothes.

Your deeply-drained starter battery is probably sulfated now. It won't be able to hold as much charge, and so won't be able to put out as much cranking current. It's worse when it's cold, so you may find it won't start again the next really cold morning.

Take it to an auto parts place once it's fully charged and they'll test it. The result will be in CCA (cold cranking amps). They can advise you whether you should replace the battery.

There are several different types of chargers out there. Some are pretty dumb, sending a fixed voltage to battery over time. That will do the job of charging up a dead battery, but if you leave it on the charger too long, it can boil the battery fluid. Some even have the ability to supply a lot of amps, so they can be used to jump-start a car if you don't have another car handy.

Smarter chargers have a circuit that moderates the output over time, to bulk-charge the first 80%, and then gently bring it up to full charge, which is something lead-acid batteries like.

Even smarter chargers have a program to de-sulfate a battery, although it takes a long time. Your car would be out of commission in the meantime.

To keep batteries topped off, a smart trickle charger like the Battery Tender is a good choice. I like these for vehicles that side idle a lot of the time.

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