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[on:]

My friends car has a dead battery. We don't know anyone around here who could help us immediately, but need the car asap.

I have a 12V, 17Ah Lead Acid battery, which someone left at my place about 18 months ago. It may or may not be charged. The only multimeter I have is rated for 13A, so I cant check it.

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Should I just hook up the batteries and see what happens? Is there any way I can check the charge of the battery? I have a ton of electrical equipment lying around, but none of it is rated for high currents, and I am a bit skeptical of experimenting...

Any suggestions?

Thanks

p.

[Reply #1 on:]

I think a 17Ah battery is a little underpowered compared to typical car batteries (I think they're in the ~50Ah range). But if it's fully charged it might work.

Your multimeter's current rating is not important, just set it to voltage measuring mode and measure the open-circuit voltage of your maybe-good battery. If it's not near 12V it has an even lower chance of working, as that indicates a non-fully-charged battery.

If you're careful, then yes, you can just hook up the batteries and see what happens. You do need big thick booster cables (else you'll lose a lot of whatever power you already have in the wiring, and in the worst case it will catch on fire). And make doubly sure you connect + to + and - to - (preferably, the dead battery - is not connected, but instead you connect the booster cable to a metal chassis point, like on the engine block, which is also -).

Wear eye protection, etc. etc.

--
The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

[Reply #2 on:]

I agree with RuggedCircuits.
I would add: If the battery has been lying around for 18 months it has to be of a very good quality battery to still be charged.
Good luck
Jantje

[Reply #3 on:]

I have two friends that independently have had a car battery explode.  Fortunately, the end result in both cases was damaged clothing.  The point of my post is...

>>>>> Wear eye protection, etc. etc. <<<<<

[Reply #4 on:]

thanks for the suggestions guys. seems like the discussion is mute, as the battery is dead.

yeah... eye protection... its important. i learned that one the hard way...

I still remember the face of the lady at the reception when I told her that I had hydro-chloride acid in my eye :-D
I got lucky, but it changed my perspective on freak accidents...