The FJ-X2m should only be charged with a USB-C to USB-A cord like the one included with the trigger attached to a USB-A port charger. The FJ-X2m will always function best with a charge level above one bar. Keeping the battery charged above that level will also extend the number of charging cycles the internal battery can provide. Best practice is to charge the FJ-X2m fully in advance of an important assignment or full day of studio work.
Though even with all features enabled you should expect thousands of triggerings from a single charge, using certain advanced features on the FJ-X2m and FJ400 will deplete the battery quicker. Settings that can affect battery charge include: Canon RT camera selection, Bluetooth "ON", FJ400 settings menu M →TTL "ON".