Power runs out faster, and the rate at which it runs out depends on the settings on which the weapon is fired. It can last for days of continuous use on marker setting, or several seconds on full power. You can connect it to a backpack battery instead.
The gas canister can last several months in the field. Therefore, there isn't a need to integrate it with the battery. Its replacement is a logistical concern rather than a tactical one.
The gas you use would be plasma and the batteries would charge the plasma, creating charged particles that, on impact, mini explosions, heating up the area. Devastating against armored and unarmored targets.