its a problem with the BCs, cause they have to use lvl9 and 10 weapons to be effective. and lvl 10 battleship weapons are by nature a lot less efficient than any other weapon. their energy consumption is waaay to big for what they gain for it - yet, its all for the balance, which works out somehow. ( excluding the mortars - which do enough boom for the energy )
in theory - a battlecruiser could get to a safe distance when its energy is depleted, they go at 140, while a battleship cannot go faster than 90. ( and engaging cruise = you lost, no matter what ) - but not sure if that works out in favour of ship balance.
since we just tested the battleship vs. BC. i think the BB would have won - but the BC did a lot more damage than i expected.