Power Source Poll?

[biglakeexile]

I went through the gamut of power ideas before settling on running 120VAC from topside to the ROV. Here's why, voltage drop. Everything on my ROV runs on 12VDC, draws about 12-15A and thats tough to push down a 300ft tether. So I run from 12VDC topside from lead acid (the batteries on my boat) to an inverter (120VAC) then down the tether (an nice, light 18gauge 2 conductor) to a switch-mode electronic power supply in the ROV and back to 12VDC. The switch-mode power supply is light, efficient and they're getting more and more available all the time.
Weight was a careful consideration when I built my ROV, as I want movement and dive/surface to to work as well as possible. So that and runtime meant on board batteries of any kind, even the wonderful Li-Po batteries weren't going to cut it.
I think unless you're aiming for depths less than 75ft or so, there's no better way to go. If I was making a pool/pond ROV I'd certainly do 12 or 24VDC for simplicity.

[soulreaper]

Im running 11.1 volt lipo batteries. The same batteries that I use in my RC airplanes, and cars

[Never prototype]

Turns out mag light makes a rechargeable ni-cad for their flashlights and the 6volt 4ah ones can be had for around 20 bucks. You can also find the same batterie in emergency power supply for flurecent lights if you can get to a junk yard. Find 2 and you have your 12 volt system with 8ah of capacity. The best part is there shaped perfect for our use. IE long cylinders.

[Seawolf]

I run a 12v, 15AH lead-acid battery. It's the largest one I could find that would fit into a 6" diameter pipe.