I need to solve a similar problem with a lead-acid (supposedly deep cycle) battery that I'll use on occasion at my camp. We have 110 vac all season but I want the backup as well as the 12 vdc to run radios, etc.
I figured that there must be some well verified knowledge on how to best "maintain" a battery. I discovered this site -
**broken link removed**
The information seems reasonable and I suspect that there is more information like it. Things that appear to be important - for a lead-acid battery:
Knowing battery condition in terms of charge - fully charged, discharged, etc.
Temperature of the electrolyte.
Charging current/voltage and subsequently the changes that are seen in current/voltage as the battery charges.
It looks like, for best battery life/performance, that there is an appropriate amount of charge (in terms of voltage or current) to be applied for a given condition of battery. A battery charging scheme incorporates some intelligence may or may not be justified. It would appear that a PIC or some other simple controller could be the heart of a very effective battery charger.
I'll share whatever I come up with in the future even if it is to copy what others have already done (as I am sure they have).