Do be careful about riding the bike til the batteries get too low. The controller probably has a circuit that will shut off the motor with low power, but lead acid batteries still have a limited life when they get heavily discharged.

My old car, which I only drove on weekends, used an AGM style battery like the four in your bike. All I had to do was forget to turn off an interior light and the battery would go flat. One instance would take about a year of life out of the battery. Twice and I needed a new one.