We were in the parks with dead batteries, a kind CM in one of the stores (Gear Works at Epcot) replaced them, no charge. Each pin came with an extra set but this was not enough to keep them going for a week. Bring lots of batteries!
another example of what sets WDW apart from other Theme Parks!
If I went to a shop/store at Hersheypark or Sea World with a similar problem, they'd be at the cash register faster than I was able to type this email...