For my electric bilge pump, the battery will go in the small compartment behind the compartment accessible through the day hatch. I am wondering if I should (A) mount the battery low (it will be in a waterproof Pelican case and, besides, my day hatch seems to never leak so I am not too worried about water) so that the little bit of extra weight will, if anything, lower the center of gravity and contribute to primary stability, or (B) mount battery case approximately half way up the bulkhead, near where I would guess the center of axial rotation would be so that it would have a rather neutral effect on boat performance. Since I weight 200 lbs and battery will weigh 2-3 bs maybe, perhaps the effect on boat performance would be imperceptible but, anyway…thought I’d ask.
low and center
In general, keeping weight low and center is bets. And center is not just left-right, but also front back. usually right behind a paddler’s seat is the best place.
That said, 2-3 pounds isn’t a huge amount, so won’t impact it too much. And because it is something that doesn’t like water, I would consider the half way up the bulkhead, so that if some water did get in the hatch, the case wouldn’t be sitting in it. Dry cases are the best waterproof option, but still not perfect. A little sand in the gasket could let water in.
Keep in mind that you do need to access the battery to recharge, so that should also be a consideration in placement.
why use such a heavy battery
I used this one 9.3 ounces http://www.hobbyking.com/hobbyking/store/__25515__ZIPPY_Compact_2450mAh_4S_35C_Lipo_Pack.html
here is is my install why ad 3 pounds of battery my WHOLE setup ads only 3 pounds. http://www.pbase.com/dc9mm/kayak_bilge_pump
Don't worry about the higher voltage my pump same as yours can handle it no problem.
Modern batteries
Technology is amazing, and it's revolutionized batteries, too.
I'm using a Tenergy LI 18650, 14.8v battery to run my Atwood pump. It weighs in at slightly under 7 ounces.
Forget that multi-pound battery and don't worry about placement that much--you are not going to notice the affect of a half pound on the stability of your boat.
~~Chip