Normally on the origination MB, and the MB 2.0 the battery normally lasts about 2+ years. You can't replace the battery on either version. That's why Disney made the MB+ with a rechargeable battery.
Even with a dead battery or the drained battery on the MB+, a MB works for every touch point. The only function that is not available is access to long range RF communication for select attraction pictures or interactive guest interactions in the parks.
No a
Disneyland MB will not work in the WDW MB system.
ETA: still learning to spell and type English words...
Dave