The rules list the Battle Cruiser in the Cruiser meta-group. To accurately model historical Battle Cruiser you would need to call it both Heavy and Fast, but that's a bit on the munchkin side.
So a category of Fast Warship might suit better. They would _not_ get the large warship bonus to shield grids as traditionally Battle Cruisers were lightly armoured.
Real naval architects found designing battle cruisers rather tricky as well...
"And all I ask is a tall ship, and a star to steer her by."
"Though a cloaking device, pulsed phaser cannons
and a full load of quantum torpedoes would be quite nice too."