On Fri, 15 Oct 2010 08:19:56 -0500, Rick Morel
wrote:

Wayne, the 50% rule doesn't really apply to golf cart batteries. Back
in my electric car days there was a "trick" we used when we were
stupid and came to a stop from totally discharged batteries. Wait 10
to 20 minutes for the batteries to "self charge", then play
egg-on-accelerator and we'd get another mile or two. Wait and repeat.
Sometimes it took three or four of these cycles to get home.

Having said that, it's a good idea to limit to 20%, simply because
most inverters will shut down around that point.

I'm sure that it's possible to get away with an 80% discharge for some
period of time. I've seen some fairly convincing life cycle charts
however that seem to indicate greatly increased battery life at the
50% level as opposed to 80%. I like to baby our house batts as much
as possible given the expense and difficulty of replacing them.

See "Cycles vs Lifespan" at:

http://www.windsun.com/Batteries/Battery_FAQ.htm

http://img32.imageshack.us/img32/9595/batterydod.gif

(from site: http://www.mpoweruk.com/life.htm )