What recommendations are there for the battery pack?
Battery pack is, from my understanding, 2 tubes of 4 standard C batteries each, providing 12V in total.
Probably could be replaced with a standard 3 cell LiPo, but more than an electrical problem this is a buoyancy problem.
The 8 C batteries give the right balance so that the ROV is well centered and neutrally buoyant.
You could fit the LiPo battery in the sealed area of the ROV and add wights to the battery tubes to make the ROV bouyant again.
If it fits
Also must check how much a LiPo would last compared to standard C batteries.
The voltage and capacity of a C size battery depends on the battery chemistry and discharge conditions. Alkaline C batteries can hold up to 8,000 mAh, rechargeable NiMH C batteries can hold up to 6,000 mAh, and zinc-carbon C batteries usually hold up to 3,800 mAh. - source Wikipedia :D
If we could fit two 4000mAh 3s (11,1v) LiPos in parallel = Problem solved. I think it would last even more than C-battery, because i highly doubt that the batterys that you get from shop have 8000mAh and lipos have very high discharge rating.
If we you could make battery box of LiPos that would weigh as much as C-battery right now, we would definitely beat 10000mAh mark.
Best LiPos on the market are turnigy nano-techs: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11927
For that we would need 50mm ID tubes... I think this is doable... I'll try as soon as I get to build the thing.