Issue / Question
ET50 ET55 tablet will not turn on or charge from Powerpack (expansion back) battery.
Resolution / Answer
Powerpack has sleep feature so that a while after no current has been drawn from it (threshold 10 mA), it will go to sleep.
This will result in tablet not detecting it (no voltage out from Powerpack). Powerpack wakes from sleep either with button press, or when tablet on wake signal is generated from accessory USB.
PMIC threshold for power on is 3.6 V with Powerpack so device battery has to be over this threshold to boot.