Lyman. The batteries may also be required for (fairly) normal ops. You're forgetting a reasonably common scenario. Powering up a dead aircraft! While it may not happen that often there are certainly cases where the aircraft will be powered up using batteries alone. Allowing for a start sequence of perhaps 90 seconds and certainly massive current draw on the APU battery, it will be seriously depleted after an APU start. This is why it needs to be charged rapidly.
Your comments on this display a lack of knowledge of airline operations & battery construction techniques among other things.
As a general winge I'm also amazed at the rampant speculation and even conspiracy theories displayed in this thread. Let the NTSB do their job then perhaps we can speculate as to how Boeing will remedy the problem.
