Battleships are not common in space navies because they are expensive to build and keep operating. Entire squadrons of cruisers can be built for the cost of one battleship.
However, a cruiser squadron cannot match the firepower of any capital ship. Massing often more than a million tons, they are usually spherical or egg shaped to allow easy in employing facing changes and weapons use.
They require little power for hyperspace travel, meaning their dozen or more fusion plants grant them immense power to operate weapons and shields.
Unfortunately, they need that power given that bigger shields need more power and their mass limits their speed. Few battleships can manage even 1G of constant thrust and they are vulnerable to drones that might penetrate their shields, hence the need for escort frigates and the like.
Base Abbreviation: BB
Tonnage Range: 500,000 - 1.5M tons
Common Maximum Acceleration: 3-5 G
Common Endurance: 100-500 G-hours, F11 sufficient for 3,000 FPH
Common Power: 2-5 dual-use toroidal fusion plants/torches (20 terawatts each), 10-20 single use toroidal fusion plants (20 terawatts each)
Common Shields: 40-100 500/5 gigawatt multiphase generators arranged at all facings
Common Armor: Very Good (multiple 200-megawatt hits or a single 1-gigawatt, resistant to HE warheads, barely useful against nuclear warheads)