Originally Posted by Piper19
A non ER 757 main battery will give you 30 minutes of power (40amphours). On a ER version, you also have the HMG, which powers the hot batt bus for unlimited time, thus the battery will be charged all the time.
- getting slightly off topic here? The figures you quote refer to a main generation failure situation, not a battery charger failure, in which we have established the busses will be powered normally, and also the HMG cannot 'maintain' battery charge, but merely reduce the drain.