I just saw his: http://www.goalzero.com/p/148/goal-zero-switch-8-recharger/22:1/ in a tech expo at work. Lithium no memory, 5v output, easy rechargeable - without complicated systems, 91 gr. weight, long lasting output , water resistant - not proof - casing and only 40 bucks … only problem has a USB out put only so some “tampering” needs to happen to connect it to a voltage regulator …
Could work on some larger vessels?
Why bother, there are plenty of Li. receiver batteries more compact and cheaper with no surgery needed.
Could work on some larger vessels?
It’s cool…but why?
I’m using 2s Lipo (2100mah) packs on 30 lb. 2m ACC boats. These packs are about $20 online. This powers Futaba receiver, 2 hi torque servos, and a very hard working RMG Smartwinch all running at direct battery pack voltage. Battery life is around 4 hours or more. Chargers either 12v or 120 can be had for as little as $20. Recharge in about 30 minutes. Amazing progress vs. nicads etc. 20 years ago. 
Bill
CT,USA