I'll add to this conversation................I purchased a 3EE AGM Battery from Antique Battery Co for my Avanti and kept it on the correct charger that Antique Battery recommended. It lasted 14 years! Yes it is expensive, but do the math, not bad over 14 years. Plus no concerns regarding acid spills or leaks. BTW, this 3EE battery weighs 40 pounds. Has a tar top, and six caps, to make it look like an acid battery.
I recently ordered a replacement battery from Battery Central Mall 804-861-0165. Wayne at Battery Central Mall Mall explained that Antique Battery was sold and the new owners changed the name to Jim's Battery Manufacturing Co.and Battery Central Mall is a retail vendor. Took about a month to get my battery. The shipping carton is excellent. The battery is in a heavy cardboard box. That box is then put in another heavy cardboard box and completely surrounded by layers of styrofoam . Ships via UPS. The cost delivered is around $450.00 as I recall. If this one lasts 14 years the odds are that I'll die, before the battery does!
John