Our keyboard player got on stage (after a full soundcheck) and had an error message on her P9HW that said “move battery position”. She pulled the battery in and out a few times and got it working. I couldn’t find a reference to this in any user manuals.
This is intended behavior of the P9HW.
There is a very small chance that during startup the P9HW cannot read the HDQ "lines" on the SB900 battery. HDQ are the lines that look like prongs in between the voltage contacts.
The HDQ lines communicate with the P9HW microprocessor to inform the user about battery time in hours/minutes/seconds, temperature, and health. If the SB900 is inserted too forcefully or at an unorthodox angle, the HDQ lines can fail to fully connect.
In theory, the P9HW would still work without the HDQ connections, but the P9HW would treat the SB900 as two AA alkaline cells. This is not desired for optimal operation.