High-voltage cutoff for battery charger necessary?
Just do it right!







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Adjustable voltage regulator.

Use a proper voltage regulator. The LM317 is an adjustable voltage regulator. Adjust R1 so that the output is 7.2 V before connecting the battery. Pedal like mad.

A 1 A charge rate at 12 V from the generator will be 12 W. A passably fit cyclist could generate 100 W for a sustained period.