The Mindstorms battery packs have been wearing out lately. In the interests of being environmentally friendly we are repacking them with cells from Battery Space.
The cases are held together with aluminium rivets which have to be drilled out to get inside.
With around 20 battery packs to open: I wrote a quick program on one of my friend's CNC machines to do the drilling for me. Each pack took less than 30 seconds to open as a result.