You could install1 battery at a t time and if fully charged each one would show a full charge. If 1 of the batteries was not turned on it would not turn on the bike. Seeing the lit LEDs from above should enough BUT 1 time I had both batteries on but I think it was the rear one , could have been either , was not fully seated and was not being used by the bike to power it. I always use the keys to install and uninstall the batteries , dont seem to fully seat by slamming them in place
