Cost effective to me was Sams club gc 2 for about $87.00 each. 4 of them. 600 watt zantrex prowatt inverter with remote wired pendant in bedroom. 40" Vizio led and 24" vizio led in bedroom. I have 2 blue seas battery switches so it can charge one bank from the progressive dynamics 4655 (55 amp) converter and the other bank from a Quick Charge 1250 950 amp) battery charger. I can charge both banks from either charging sources or individually from either source. The 1250 will do 15.3v and the 4655 tops out at 14.4v (?)
I have never tried agm so cant say. I dont find wet's to be a maintenance problem but some dont like them. Mine have been in service for 8 months and still look new. I have added a little water twice in that time.
Will your converter/charger do 15 volts?
Your charging source, length of cable, size of cable will play into your charge times.