The term "battleship," on SRTMOO, comprises just about any armed carrier of units, ranging from a wanzer-equipped dropship with a pair of gatling guns to a Macross-class transforming colony ship with an absurd number of weapons and gimmicks. The following are some of the most common general types of battleships.
The Macross and its related classes consist of all deep space exploration and habitation vessels patterned on the SDF-1 Macross, a transforming alien battleship which was refurbished by Earthnoids after crashing on Earth. For decades, these were the primary deep space exploration vessels of the Earth Sphere, thanks to their Fold engines. These engines were recently reappropriated by Neo-Colonial citizens to escape after the fleet recall, however, leaving most Macross-class vessels stranded in the Earth Sphere. Even a small Macross-class vessel is several hundred meters on each dimension and carries an essentially arbitrary number of mobile weapons.
Since the advent of the mobile suit, MS carriers equipped with Minovsky Crafts have been some of the most consistently-used, effective battleships of the Earth Sphere. Typical battleships of this style carry between 6 and 10 size M units, and are usually also well-equipped combat platforms in their own right. Common gear at this scale includes mega particle cannons, missile bays, and CIWS turrets.
It is relatively cheap to make an MS carrier that does not need to work in atmosphere, and a fair number of factions still use these. More commonly in the modern era, however, MS carriers are equipped with Minovsky Crafts, enabling them to achieve lift within atmosphere.
Before the development of the Minovsky Craft, land battleships were a common solution to the need to transport mobile weapons across the Earth, and remain a somewhat popular choice due to their extremely low cost compared to other options. They also tend to suit cases in which there is no intent to bring the weapons to space, such as most MULS-P derivations and many mobile suits. You could theoretically outfit a land battleship with a Minovsky Craft to make it a viable air and space solution, but this usually defeats the point.
Land battleships usually carry between 4 and 8 size M units, or a lot of size S units.
For countries with small militaries and sea access, aircraft carriers remain a popular option. They are extremely thoroughly-explored technology, even cheaper than land battleships, and easy to refit with whatever weapons you might happen to want. Aircraft carriers have some of the highest carrying capacity of any currently-used vessel.
Submarine warfare has remained a major component of warfare into the present, and somehow, spacenoids are really, really good at it. Submarines usually carry only a few mobile weapons, but dominate the water and even fairly successfully aggress against land-based targets. Submarines usually rely on missiles for the majority of their offense.
While not really battleships as such, dropships often fulfill similar roles at smaller scales. Usually, a dropship has only light armament and carries 2-6 MULS-P or MULS-P2-compliant units. They usually only mount solid-state weapons, and are more effective for quick insertions than long campaigns.