Thingiverse is a website where people publish and freely share plans for parts that can be printed online (for a fee) on a 3-D printer.
User BillyBean on Thingiverse recently published the plans for a G5 battery cover, for DIYers intending to replace their G5 transmitter battery:
As a reminder, if you plan to replace your G5 transmitter battery, you need to be use xdrip/xdrip+, since the Dexcom app will recognize a used transmitter and refuse to pair to it.