Capacity and Usage
All ranged weapons use ammunition, and melee weapons with the powered weapon ability require batteries to operate. These scaling weapons have a starting ammo capacity and usage values based on the type of ammunition used. These values sometimes increase at higher item levels, representing the weapon’s larger magazine or more intense energy needs. In addition, the weapon’s type, perks, and drawbacks can affect these values.
Batteries: The weapon has capacity 20 and usage 2, requiring a battery to operate. At 7th level, the capacity increases to 40, and the weapon requires a high-capacity battery. At 12th level, the capacity increases to 80, the usage increases to 4, and the weapon requires a super-capacity battery. At 17th level, the capacity increases to 100, and the weapon requires an ultra-capacity battery.
Mini-Rockets: The weapon has capacity 6 and usage 1. At 3rd-level and every 3 levels thereafter, the capacity increases by 1. These values are typically appropriate for flare and shell ammunition, too.
Petrol: The weapon has capacity 20 and usage 2. At 7th level, the capacity increases to 40.
Rounds: The weapon’s capacity is based on its weapon type: 2 for sniper weapons (already factoring in the reduced capacity applied to sniper weapons), 8 for small arms, 16 for longarms, and 32 for heavy weapons. At 7th level, you can increase the weapon’s capacity by 50%. The weapon’s usage is based on its weapon type, too: 4 for heavy weapons, and 1 for other weapon types. Other physical ammunition like darts and flechettes typically use these same values.
Source
Starfinder Enhanced pg. 144