If the pilot starts the APU during ground start-up and shuts it down without starting the right engine, then the ground crew must recharge it manually. Otherwise normally the APU should recharge itself once the right engine is up and running. Starting the left first won't recharge it as it is not connected. Not sure why the warning is on in flight though.
Lähetetty minun ONEPLUS A6003 laitteesta Tapatalkilla