I have one of these that I use to charge my Optima cranking battery -
http://www.marinco.com/en/2612a
For my two trolling motor deep cycles I have an on-board 2 bank Minn Kota charger, 10 amps per bank. Depending on whether you have flooded wet cell or AGM batteries make sure your charger is compatible. I hear good things about the NOCO Genius chargers and they are more compact and lighter than most.