Why not go for the 12 AH battery that is the same dimensions and only 90 cents more. I'm not sure if I would need that much power.

I had been considering using 9 "D" cells, Eveready had them at 18AH and the "C" batteries are rated at 8.35 AH. http://data.energizer.com/ The pro about using alkaline are that I can pick up some anywhere, but the cons are that they aren't rechargable (Unless I buy the big $ rechargables), and that I'd have to link them all together.

I think the gel battery is probably the way to go.

: I figure my cockpit will hold around 100 gallons. At 400 GPH (figure a 1.5
: foot head) that would take 15 minutes to empty. A 10 AH capacity sealed
: lead acid (gel cell) battery would power that (at 2 Amp rate) for 5 hours
: continuous. That's enough to empty my cockpit about 20 times. The battery
: weighs 4 pounds and cost $16. The pump $15, a switch and some wire. I
: wouldn't worry about sealing the battery (at 13.5 volts it's not going to
: produce much current when submerged unless it's in mud and mostely iron)

: That is looking like a pretty good option! The weight is the only thing I
: don't like

Why not go for a smaller AH rating (smaller size) and only use it for emergencies, but give yourself enough cushion to empty it several times (say a 5 AH battery).

: but a battery like this could be useful for other things also.

Like a loud airhorn and maybe some running lights? :-)