The ideal charging rate for most batteries is 6 to 8 hours. Also, a
battery should never be discharged more than 80% (includes deep cycle
types). The Optima being an absorbed glass mat battery (AGM), is
especially prone to damage if it is charged at too high a rate. The
alternator running at 14 volts will push 20 amps into the battery
through most of its charge cycle. So there is little value gained going
through this exercise. You must also note that if the battery is fully
discharged, it will be slow to accept current at the start of the charge
cycle. This is due to the fact that a fully discharged battery has water
instead of acid in it. The water does not conduct current well. This is
also why a discharged battery will easily freeze in winter.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of lchase
Sent: Friday, January 25, 2002 11:37 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Shorten Aux Battery Recharge Time

Folks,

Please tell me if there is anything wrong with the following assumption.

I want to shorten the recharge time for a fully discharged Optima 750
Deep
Cell Battery to around 2 hrs while driving.

What if I power a 20amp smart charger (Made for Deep Cells) via my
existing
1000 watt inverter thru a switched circuit that allows the inverter to
draw
its needed power from the alternator while the engine is running. If my
calculations are correct, a 20 amp charger should fully recharge this
battery in around 2 hrs. If the 1000 watt inverter uses too much power
and
puts too much extra load on the vehicle 12 volt system, I could dedicate
a
smaller inverter just for the Battery Charger and eliminate the need for
a
switch.

What am I missing here?