Not every LR owner ...
Anyway what Mr Fridge is commenting on is this:
If this was QI ...
Anyway, starting a given engine at a given temperature, etc. takes the same energy no matter what. In fact, a bigger (more cold cranking amps (CCA)) battery will do better than a small one at low outside temperatures, as it will spin the engine as fast (or faster) for longer. Both the big and the little battery will lose the same amount of stored energy, which the alternator will try and put back. The problem is when the small battery can't supply the current required for the duration of starting the engine, in which case it will suffer damage as it becomes heavily discharged, or the alternator is too small for the engine.
Summary - get a battery that will at least source the required CCA (about 400A for an LR diesel, slightly less for a petrol) and will just physically fit in the battery tray. If you find that the battery doesn't get charged up fully between starts, fit a bigger alternator.