Aircraft will not accept ground power, Hot Battery bus circuit breaker pops behind Captains seat when starting APU
Repair bad ground for aircraft battery. GD3252-DC
With no power on aircraft, close battery switch, if you do not get the normal battery powered lights and systems.
Check the P18-5 panel behind the captains seat for the Hot Battery bus circuit breaker open. If it is open, close this circuit breaker and attempt to put on the battery switch again. Even if it comes on. You should go directly to the battery and remove the connection and verify a good ground at the plug. It is required to be .001 ohms per the WDM 24-31-21. In this scenario you could put on ground service then apply aircraft power and it would come on. This is because you are back powering the Hot battery bus then holding it on with DC power that is converted from AC.
A bad ground will have intermittent problems with different systems. It will cause the Hot battery bus breaker on the P18-5 panel (C22) to open during APU starts, it will cause problems with applying power. It could cause the Gen BUS off light not to illuminate. It will make it appear as though the Battery is dead. All these could be indications that the Ground for the battery is bad.
WDM 24-31-21, 24-56-01 DWG #69-78615-3
Thanks to Tom S. for his input !