Hi Nigel,

it depends on the type of battery, you are using:

automotive batteries are made for short high current during starting, they
should not been discharged more than 60...80%. In your case 80 AH
discharging will be critical.

marine batteries are made for slow and long discharging and they should not
been discharged too much. Gel batteries should not been discharged more than
60 %, wet batteries not mote than 80 %.

Take a look at the voltage, if you have a digital meter: battery voltage
lower than 10.8 V will damage the battery (deep discharging).

regards

Juergen

"Nigel" schrieb im Newsbeitrag
...
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?