I own a drag car. 2 years ago I bought a 16v AGM battery for it, along with "The V" battery charger. Works well. The charger is DESIGNED for AGM batteries only, works for 12v and 16v.
Anyway, I pulled the Optima red top out of the race car and used it in my boat. I charge it up after each use with "The V" charger. And this time of year, I use the boat about once a week...more often soon as the nights are getting warmer and I can go after work.
I run ONE battery. 1542 boat, 25 Yamaha 4 stroke Electric start, nav lights, courtesy lights, Q beam, and Motorguide W45 wireless trolling motor. Ran the trolling motor almost 7 hours straight last Monday on lower speeds (trolling/bass fishing) and the outboard motor started right up when I was too sunburned to fish any longer.
And to think that I bought that Optima in Feb 2001. IMO, hard to beat an Optima battery.
Next project...going to try the 16v battery on my old hand control trolling motor. Should be interesting but I am not expecting anything out of the ordinary as ALL of the 12v accessories (datalogger and all) in the race car work find on 16v, which charges at almost 19v when the charger is plugged in. Headlights are brighter, taillights are brighter, and the E-fan sounds like it's cleared for take off.