It's the wrong chemistry for the type of environments and stress that such equipment experiences, if they can switch to LTO or other type of more robust batteries then it should be fine. Tanks and armored vehicles should all become hybrid because besides increasing range on the same sized fuel tank with relatively small percentage of added weight, it will also increase acceleration, improve responsiveness, make them quieter and difficult to detect when stalking behind cover or scouting and reduce maintenance cost of the engine as it run closer to optimum rpm most of the times, other benefits also exist with regards to powering more powerful electronics easily or enabling new electric powered equipment previously impossible to use because it couldn't provide enough power (think radars, Lidars, lasers, masers, microwave emitters and other sensors or weapons). If there is a big downside is likely cost because of many things related to producing more robust versions of a commercial product.