I do all of mine.
Bought a tool kit from Harbor Freight (
8 Piece Watch Repair Kit). I found, depending on which watch, I either the tool to unscrew the back and the one to open the press together cases. The magnifying glass and tweezers are handy. The screwdrivers suck
I buy the batteries in packs of 5 from e-bay for less than $1 each.