Can you add a “only when on battery” option for the “Run according to time schedule” setting, under “Run Conditions”?
This way, Syncthing would run full time while charging, and run according to time schedule only while on battery.
If possible, add also the “Sync within first 5 mins of hour if “Run according to time schedule” is enabled”. That is really a good idea for those who do not have a central server running full time.