Charging car battery from a car

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Mon 17 Mar 2008 22:24
Charging car battery from a car - Welliesorter
Maybe this really belongs in Technical Matters but I'm sure there will be plenty here who know the answer.

A friend (really not me) has a flat car battery which he needs to charge. This is used for an electric mower.

He's wondering whether there's a quicker method of charging this than connecting it to a mains-powered charger. He's thinking in terms of using jump leads to connect it to the battery in his car. If he does this, will it charge from the alternator if he runs the engine for a while?

Swapping the batteries isn't an option.

The car in question is a '97 Ford Escort if that has any bearing on the answer.
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Mon 17 Mar 2008 22:41
Charging car battery from a car - Screwloose

Lots of variables here; how flat is this battery for starters? If it's sat flat for more than a few weeks, then it's probably scrap anyway.

The car will charge it - if you leave it running for about five days..... A proper float charger would be - so - much easier....
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Mon 17 Mar 2008 23:36
Charging car battery from a car - Welliesorter
Thanks for the near instant replies!

To be honest I don't know why he thinks it would be better to do this than to use a mains charger. I think he imagined it would be quicker. Not sure why.

I'm guessing from the responses that there's more than one type of mains charger and he's probably run out of patience because he has one that's intended to be the trickle type.
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Mon 17 Mar 2008 22:50
Charging car battery from a car - FotheringtonThomas
Get a decent charger, for what you/he wants not a "trickle charger". It'll save a lot of hassle, won't fry your battery or circuits, and might be useful once every so often to charge a car battery being used as such!
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Tue 18 Mar 2008 06:34
Charging car battery from a car - grumpyscot
Not all electric mowers use 12v batteries - charging with a 12v charger or via a car will.... well, let's not go into the damage an exploding battery and spraying battery acid can do...........

Besides not all batteries are designed for "quick charge" - i.e. from a car alternator - many batteries such as those found in mowers are designed for slow charge - desirably from "flat" too.

Edited by grumpyscot on 18/03/2008 at 06:35

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Tue 18 Mar 2008 08:27
Charging car battery from a car - Cliff Pope
If he wants to use fuel running a car engine to charge a battery to use in an electric mower, he'd be better off with a petrol mower in the first place!
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If you cover no more than 100 miles per day and have easy access to a charging point at home or work, then an EV is ideal for you.

Is an electric car right for me?