Torque reduction starters. Smaller package with greater torque output, = less current required at peak draw and constant run with motor already in motion.
Basically the battery is mainly there for instantaneous electrical loads and less starter amperage required = less total maximum load. Alternator takes over once the car is running.
Honda Civics of the newest variety have super small batteries because of the low torque required to crank over their motor and accessories.
If however you have power seats, larger radio option, electric sunroof, etc; you can expect a car to have a slightly larger capacity battery if the option is listed for it. It's always a good idea to have a little more available from a battery within reason.
I don't understand guys running super small batteries in road cars. That's just me. I leave lights on, drive in colder weather, etc. I deal with broken cars all day, so it stands to reason I don't want to strand myself, even more than the next guy.
I guess that's one of the culprit that needs to be considered, the starter.
I've pulled out my starter was able to compared it. Our was so heavy and bulky and other are smaller yet more power and higher output, just wandering what reduction starter would fit our CSM from his younger sibling to utilize using small batteries.
I believe some Mitsu or Hyundai parts can be interchangeable
To know the clock fitment (angle of the nose), plunge depth and mating tooth style, you could cross over a smaller but more powerful torque reduction starter, but it may require opening lots of boxes in a parts store/back room type scenario. As long as the starter has at least the KW rating of the factory starters, then it is a good match. 1.2KW comes to mind. IF you have a high compression motor, or at least more compression than stock and or some additional accessories drawing on the instantaneous start motion (which most people don't), you may have to look into a slightly higher KW rating.
Better yet, contact a technical support line for a company that makes starters and see what could crossover based upon the nose cone, size of the component overall and power output. Then fitment of wiring would be the only issue - harness changes at the end or not.