Device won't power on upon USB connection when battery is fully empty
Found in PN02
Let device sample offline until battery is empty, cell protection was active (0 Volt at battery connector). Connect USB, voltage at connector remains 0 V. Area around U1 clearly warms up. Disconnect USB, disconnect battery, reconnect battery and reconnect USB: device turns on and charging starts.
(there might be a small chance the battery being at 0 V is caused by a short. But still the charger should be able to reactivate the battery.