Power is the time rate of energy use. Asking how much power is in a battery
is like asking how much velocity is in a full can of gasoline. There is no
limit implied by the spec quoted.

The Ah spec is usually given at the 20hr rate which is the time to discharge
the battery to 1.75 V/cell (lead acid battery assumed) with a steady current
draw, 5 amps in this case. For a 12 V battery this equates to 10.5 V. It is
a non-linear relationship, halving the current will not double the discharge
time. Battery manufacturers can provide curves or charts that show the
actual Ah for different current draws. The spec is intended to represent
usable capacity, since a battery can be recharged from 1.75V/cell with
little loss of life. Deeper discharges will shorten life. Not too many real
world loads are constant current. Lights will use less current as voltage
drops (constant resistance), motors will use more (constant power.)


"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?