Trolling motor batteries i have are 2 super start's group 31...i have an on board dual pro 2 bank charger( 15 amps per bank) which which charges the batteries as fishingwrench has described.
Crank battery is a group 27 super start and i use a noco 1.5 amp smart charger on it, which is more of a maintenance charger.
I have had the batteries a year with no complaints yet...i got a good price on then which was hard to turn down