Options vary from cheap lead-acid (preferably AGM-variety thereof) batteries to the bees-knees LiFePo4 lithium.
Lead: heavy, but cheap. Ez to charge. Steady loss of voltage/power when under load. Limited number of charge cycles (but not a concern really for our application).
LiFePo4: 1/3 of the weight for equal capacity, thousands of charge cycles, steady voltage/power. Charging requires oversight and/or special charger/Protection circuit board. Need to be careful when discharging, to not go below certain voltage per cell.
I lucked out and got 4 100AH LifePo4 cells on ebay, @ $80 per. I arranged them in 2 packs of 2 cells and this way I can fit it into the center compartment of my PA14. Now I have about 30 miles range on the water and don't have to be afraid about running outta juice. ever
Still carry my Mirage with me , for JIC
I posted in-depth on the subject in stripersonline, under kayaking forum, last year.