Redout
You are correct except that in the case of a simultaneous double generator failure the recommendation is not to start the APU.
FCOM 3.2.24 ELEC EMER CONFIG
In case of simultaneous engine generator failure, the probability of a successful APU GEN coupling is low. Therefore APU start attempts should be avoided, as this will consequently reduce the flight time on batteries only (by about 3.5 minutes for one start attempt).
This is because in emergency elec config with the older RATs you are left with battery power only when you put the gear down.
You would not want to be flying an electric aircraft on just the battery if it had been depleted by a failed APU start attempt. Our old friend risk assessment again
