APU
airbus says no, on most A-320 you will have rat power down to 125 kts, by then you should be on the ground then you will be on backup electric power (the batteries) the thought here is if the APU does not start then you have killed what would have been your only electric source. I guess Airbus i following Murphy's law,,,, if you are already having that bad a day, guess what will not start. but personally, I might be tempted.