So, after having a good hard look at the Deep Cycle Battery FAQ on Otherpower (thank you guys for hosting this GREAT reference!) and studying the the somewhat skimpy manual that came with my Xantrex C12 charge/lighting controller, I decided to make a few changes to the factory settings.
There are 5 basic settings on the C12:
HVD - High Voltage Disconnect
HVR - High Voltage Reconnect
LVR - Low Voltage Reconnect
LVD - Low Voltage Disconnect
Nite Lite Timer
The 2 that most concern me are the HVD and the LVD, neither of which are explained very well in the manual. The C12 came from the factory with the LVD set at 11.5v and the HVD set at 14.0v.
I'll spare you all the mumbo-jumbo and just state that I increased both settings. The HVD is now set at 14.6v and the LVD is now set at 12.1v. The key concept I gleaned from studying the info contained here: http://www.uuhome.de/william.darden/carfaq9.htm#stages
is to understand how charge/discharge battery voltage differs from battery voltage at rest. And also the subtle differences in the charge/discharge algorithms of the different battery types. I think I'm pretty close to optimal settings for my "hybrid" battery, but I welcome any insight you might have.
Cheers!
Brian