One thing to consider is relative energy densities. As an example from
today's technology, the following is a list of different types in increasing order of MJ/kg:
Water at 100M height - .001
Energy needed to melt ice - .334-.335
Compressed air (300 bar) - .5
Lithium-Ion Battery - .875 (high end) (rechargeable)
Lithium metal - 1.8 (not rechargeable yet)
Ham & cheese sandwich - 10
Wood - 16.2
AA Battery - 24-26
Coal: ~30
Body Fat - 38
Kerosene - 42.8
Car gasoline - 46
Diesel - 48
Methane - 55
C Battery - 65-82
Hydrogen (burning the gas) - 142
Tritium (via nuclear decay only) - 583,000
Plutonium 238 in an
RTG - 2.2 million
Uranium/Thorium (breeder reactors) - ~80M
Deuterium - ~88M
So rechargeable Lithium batteries are good in that they can be refilled with ordinary electricity, but they are really bad in terms of storing energy compared to wood, let alone gasoline. These numbers are why I want to put in a RTG style charger for battery powered vehicles. Similar to today's electric cars that have a regular car engine in them too to help charge the battery.
So assuming we want to convert this to Battletech, then assuming you allocate 1 kilogram of fuel for the vehicle to go 1 km, and this is done via rechargeable lithium metal batteries (1.8 MJ/kg), you would be able to go the following distances with other fuel sources:
Wood: 9 km
Gasoline (ICE) - 25 km
Hydrogen fuel - 78 km
Tritium decay - 323,000 km
Thorium reactor - 43 million km
(If you want to try comparing using Lithium-ion batteries, the above distances would be doubled)
This of course not factoring in the engine mass itself.