You can load a truck with fuel cells to extend range beyond what the current infrastructure can handle.

It’s more complicated with batteries that need to be charged. Sure, there’s a grid in many places, but if combat capability depends on the grid, it’ll get targetted. And even before that, capacity is a concern and if the grid can handle a tank battalion wanting to plug in every tank so they can be ready for whatever comes next ASAP.

Fuel cells mean they can set up behind the front lines and use power more predictably and refuel tanks quicker than gas.