Batteries will be AAs, so you will be forced to replace them.
You can buy rechargeable AAs that are pretty long lasting, so when you turn off the controller, just plug the AAs into the wall charger or whatever.
I believe MS will be releasing Li-Ion battery packs, or at least some third party will, so that should solve the problem of buying multiple batteries. If you buy one Li-Ion battery for each controller, lets say that is under $100 for about 4 or 5 controllers (and that's more than most people have anyways), then you are saving the money becaue you won't be replacing the batteries, just keep recharging them.
Yes, MS has some sort of docking station for this, I have seen pictures, but am too lazy to post them. Anyone?