The real issue is that I've not found any converter that will charge a 12v battery (6v in series or 12v) at 14.4v to 14.8v and that's what you must have to get 100% charge. Don't believe the little red LED thing, it's almost useless (how well does it read your tanks?). Go to your battery manufacturer's website and see what they say if you don't believe me. 13.6v is only a float charge level for after they've been fully charged. You must use either a solar system or an inverter that will provide these levels.
'06 F350 TD, Softopper, airbags, AeroShield, coolant filter
'10 3665RE Hickory edition, wetbolts, Firestone LTs, Trimetric Battery Monitor, 4x100w panels & Morningstar TS-45, still tweeking.