wrote in :

On Mon, 16 Jun 2008 20:24:23 -0500, Geoff Schultz
wrote:

Wayne.B wrote in
m:

On Mon, 16 Jun 2008 08:11:06 -0500, Geoff Schultz
wrote:

You should also learn that you shouldn't deep cycle any batteries.
I try not to have mine drop below 12.3V and typically keep them at
12.5V and above.

They should last just about forever with that kind of tender loving
care. We routinely cycle our inverter bank of 4 golf cart batts
down to 11.8 or 11.9, sometimes even lower. At 11.6 they are at
about 50% and I try to never go lower than that.

11.6V is about 20% and 11.8V is around 35%. Anything below 12.06V
(without a load), which is 50% will kill them. See
http://www.windsun.com/Batteries/Battery_FAQ.htm


-- Geoff
www.GeoffSchultz.org

Nope. 50% is a more or less random number picked for convenience as
much as anything. The deeper you cycle, the shorter the lifespan, but
there is no magic that happens at 50%. A battery that never drops
below 80% will last twice as long as one that is cycled to 50%. Yes,
cycling the battery lower than 50% will make it's life shorter than
50%, but it won't "kill them". A battery that is never dropped below
90% charge will last a REALLY long time compared to one that is cycled
to 50%. What you have to do is balance cost, weight, complexity, etc.
If you are willing to carry more batteries, your batteries can live
longer. AGM's can be cycled deeper than flooded batteries for a given
lifespan. 50% cycling will "kill" a flooded battery before an AGM.

It's true that going below 50% won't immediately kill them. But over
time...I just go by the rule at anything over 50% is bad for them,
especially if done on a regular basis. As has been discussed here,
batteries cost too much not to be well taken care of.

Considering how many systems rely on power, I consider batteries to be one
of the most important components on the boat. As a result I baby mine.

-- Geoff
www.GeoffSchultz.org