Short version is that you can't rely on the power grid or other centralized generation. Centralized infrastructure may not even be available, but if it is then the enemy can target it.

I'm not a tank expert, but my impression of Wehrmacht tanks vs Soviet tanks is the Wehrmacht tanks used aviation engines. Aviation engines are light and powerful, but don't have much life, were finicky, and require aviation gas. Soviet tanks were simple and used any liquid that would burn.

The US military is starting to use some hybrid vehicles to improve fuel logistics and reduce operating noise. But pure electric ground vehicles are obviously a stupid idea for combat usage due to charging issues.