With the amber daytime running light connected to the Bafang’s headlight output and the Anker flashlight on the other side of the fairing getting fewer power-on hours, it’s a good time to see how those four Tenergy lithium 18650 cells are doing:
The overall capacity is down by 10%, with the voltage depressed by 120 mV over most of the curve.
Although I don’t keep daily records, the back of the envelope reveals 150 to 200 hour-long rides per year during the last four years, so call it 700 charging cycles:
High brightness draws 1.5 A and low is 50% duty cycle, so a typical ride requires 750 mA·h = 2.5 W·h. Each cell lives for three or four rides with the LED set to low brightness and the numbers work out close enough.