NiMH Battery Options for Onboard Power

[anagama]

I'm planning to run my ROV with 2.5 amp thrusters (4) with onboard power. I've looked at a number of NiMH battery packs in the 6-10 Ah range, and they are fairly pricey (approx $180 - $250).

I found a pack of 12 D NiMH batteries for $90.

I'm thinking about just putting 10 of those in a tube, filling it with oil, and using that as a power supply.

What I would like to learn are potential pitfalls with this. Do these types of batteries offgas anything I need to worry about? Is it really true that I won't have to deal with pressure issues if I fill the battery tube with oil? What kind of oil? If I do fill it with oil, I will obviously not want to take the batteries out to pop in a charger because that would be a mess. Can I charge the batteries all at once? Are there problems I'm not thinking of? Anyway, any advice would be most appreciated.

[krigsmaskin]

you can fill the tube with hydrolic fluid, hydraway 22 or something, if u succeed in removing ALL the air it will work. if it holds a constant teprature. my tip is to connect a varible reservoir.
the simplest way is to connect a bit of a flexible garden hose, half filled, and blanked.
If the fluid volume inside your container increases it will fill the garden hose. if it decreases the hose will collapse forcing oil into your container.

keep in mind hydrolic fluid is nasty. eats some typs of plastic and rubber. and it's bad for you.
the good side is that it keeps it viscosity in low tempratures, and it dont conduct current.

helge

[Kjetil]

I did purchase 20 D batteries for USD 64. http://www.ebay.com/itm/20-D-10000mAh-N ... 27bef062f5

Plannign to just put these in 50mm tube. Just like the camera.