"Nigel" wrote in message
...
Stupid question time...
If I have a 100ah battery how much power can I expect to get out of
it... is
100ah the total battery capacity or it's useable/available capacity.
My
understanding is that a normal lead acid battery shouldn't be run
too flat,
so when is flat too flat? If I should only let my battery drain down
to say
a 90% charge, have I only got 10ah before I need to recharge?

If it is a "leisure" or deep discharge battery, then conventional
wisdom is that it shouldn't drop below 50% of charge. This sort
of battery would normally be used for the "domestic" stuff on
your boat.

A "normal" or engine-starting battery is designed to give high
current for short periods of time, then be charged straight away,
so it is more difficult to give a value.

I don't suppose that has helped much.

--
Steve Brassett