2s lipo for UBEC, what size?

[FighterCat57]

Is 800mah 20c enough for a receiver/rudder servo?

I'm thinking of using this UBEC and this battery, but have not worked with UBEC & small lipo packs for receivers.

UBEC: http://www.hobbycity.com/hobbyking/s...idProduct=3735

Lipo: http://www.hobbycity.com/hobbyking/s...idProduct=6786

Servo: http://www.hobbycity.com/hobbyking/s...idProduct=9441

Thoughts, suggestions?
(this is to work with the Castle Hydra in the Genesis that does not have BEC on 6s)
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