I couldn’t find an answer about whether the project still works without a battery, so I decided to try it out.
The battery was bloated.
Unscrew the 4 Philips screws at the bottom and open the bottom case.
Open the top case (no screw) and detach the power cable (the longest one in black, yellow, red). Careful to the touchpad cable!
Then the battery can be removed. It was glued to the main body, so I applied a little force to pull it out.
The projector still works when connected to the stock charger and without the battery. The UI shows “0% charged”. Red & blue LED flashing persists.
I noticed that my battery cable was not fully plugged into the socket on the motherboard. Not sure whether it caused the charging issue (red-blue flashing).