I assume you're talking about UPS for computers?

A car battery is a bad choice for one of these. Car batteries are designed
to give very high current for a short time, and do not like to be
discharged more than a few percent. I've seen spec tables that show if you
discharge a car battery past 6V then recharge, it loses as much as half
it's rated capacity.

A marine deep-cycle battery would be a better choice. These are made to
power electric trolling motors, and don't have the problems with a deep
discharge the a typical starting battery does.

But either way, you're opening a whole can of worms with vented batteries
in the house. Acid fumes, hydrogyn gas while charging, potential for leaks,
I wouldn't think it's worth it.

-Denny

> Can anyone think of a reason not to attach a car battery in place of the
> sealed battery in a battery backup system?  I've got a few of these
> carcasses laying about because it's always been cheaper to buy a new one,
> but a cheap car battery could breathe new life into them.  Clearly, I
don't
> want to turn it over and spill acid, but think of the backup time
available!
>
> Thanks,
> Ed
>
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