In article om,
Dave Liquorice wrote:
If say, I wanted to power a laptop this way (mains transformer = 12v
and 4.16A) how long could I expect the car battery to last?

Quite a long time 12 hrs maybe longer but I doubt that a car battery
would survive this sort of treatment for very long. They are designed
for short high current use and immediate recharge. Not for long slow
discharge to almost nothing.

(Mr Plowman will be along shortly saying his car battery based UPS is
fine thank you very much...)

Err, no, Mr Liquorice. (gawd we're a polite lot). It's not a UPS as such -
merely an emergency backup for the central heating if we should ever have
a power cut. And it uses my spare car battery, which I wouldn't run
anywhere near flat - if it were a prolonged power cut I'd swap them over
in plenty time.

You should be using a "leisure" battery for deep discharge use. These
are designed to provide all their charged over a period of time and
then be recharged.

If you can be sure you'll not anywhere near fully discharge a car type, it
might just be the cheaper option, given the difference in cost.

--
*I must always remember that I'm unique, just like everyone else. *

Dave Plowman London SW
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