Originally Posted by markopolo
Sounds like an OK plan to me. Costco used to have (and probably still does) a Group 27 size dual purpose rated 100ah or 110ah for a good price.
Measure your space and then go battery shopping.
You current converter charger looks to charge up to 13.8 volts according to some docs I looked at.
#1 - I would not leave it plugged in for extended periods at that voltage (weeks, months etc.).
#2 - I'd periodically (once a month or once per quarter) hook up an external charger that can get to 14.4 volts to make sure the battery gets a full charge every so often.
We have the Costco group 27 battery as a starting battery in our van. OK battery, definitely a dual purpose as it doesn't come up to very high voltage or specific gravity. The good of that is that it also uses very little water. Unless they have fixed it, the rating of 110ah is really reserve minutes or something, don't recall. It is actually like the other group 27 combo batteries at about 85ah, 20 hour rating.
Definitely a reasonable cost well under $100, and should be fine for the application.