Which model Powabyke?
The Euro21 has an LED voltmeter on the battery pack. The battery pack is 36 volt (3 x 12V) and when
fully charged all 6 LEDs turn on. As the voltage drops the LEDs turn off.
I haven't checked yet but I imagine that the voltmeter is calibrated to indicate from between about
30 to 38 volts. Discharging below 30V (10V per battery) should be avoided.
I don't have any long hills on my route. I run with 5 or 6 LEDs lit on the flat and 4 on hills.