What happens if I can't turn the eBike on?
One of the moving components i.e., the rechargeable battery and possibly the display, is probably not correctly engaged. Check these components by removing and reattaching them.
If you can't turn on the eBike via the display, switch on the eBike via the eBike battery if possible. The display battery will then be charged by the eBike battery.
Alternatively: Charge the internal battery of the display via the diagnostic port with a micro-USB cable (charging voltage 5V; charging current max 600 mA). Always close the cap of the diagnostic port afterward to prevent dust and moisture from entering.
If your eBike has a Purion: Change the batteries of the display. Two CR2016, 90 mAh button cell batteries are required.