Jonas.

Is the servo really essential? Could you not do it with a rc switcher. Yes I know they are more expensive than a servo however they are much better and wont break or throw off a servo horn in the middle of a fight.

I personally have 1 servo in my robot to fire my valve but it is on the top of the list of things to be replaced.

But if you really cant then go for a Rx battery. Paul Hill one of the resident Techys (people who really know their stuff) is really strongly against regulators. They cause huge amounts of interference even with supression. But if you really have to go with something like a 5amp one. That should give you some spare just incase the servo stalls.

Regards
Ian