How did they start the APU? Ground Fault?
One would assume that the main busses were still powered, therefore APU would be started from power available and not the APU bat.
How many of the replaced batteries had one bad cell? Does it matter? The question is about dispatch, and reliability.
Cannot launch without both batteries at a specific SOC. The rest is spilt milk.
Didn't we cover this already? MEL allows dispatch with APU inop. I assume that includes APU bat inop.