Hi,

you shoud not discharge more than 50% of nominal capacity. Discharging more
than 50 % will reduce the number of possible cycles for
charging/discharging. Gel-batteries can be discharged more than 50 %, up to
80 % without reducing cycles.

50 % of discharge are reached at 11,8 volts at normal batteries and 12,2
volts at gel batteries.

If You want to start your engine for charging, be sure, that you don`t
discharge too much, because an empty battery won`t start the engine.
Starting the engine will discharge battery additionally and you reach depp
discharge area, wich damages the batterie. So the voltages befor are
absolutely minimal values.

Best will be to have 2 batteries, one for the engine, one for your power
consumption on bord.

regards

juergen

"varnish" schrieb im Newsbeitrag
. uk...
I've got a 300AH domestic battery bank and monitor the voltage across it
while cruising. It's usually around 12.8 when charged. What does it
have to drop to before I run the engine to recharge it?