Well, thanks for all your very informative answers, they are much appreciated.
This clears up a few things, especially regarding the Voltage versus potential lifespan.
I know I will eventually open up the gearbox and check it out, as I always do that for everything anyways (I enjoy seeing how things work with my own hands and eyes), but for the moment, or for this summer season, I want to concentrate on getting decent equipment that will last, upgrades will wait for next winter.. so I want to have good stock internals. As for battery, I will do more research, but 8.4v 1500mAh seems to have a good price/"quality" ratio.. not too much stress on parts, and still giving a decent amount of shots (I plan on always having a second one as backup).
Any more information would be welcome, and I thank it in advance.