I picked two up at a fallen battlefield but can't seem to work out what they do and how to work them.
Timmy is correct. Carbine is a ranged weapon.
From the wiki
cooldown: 1 seconds
use cost: 1 battery
creation cost: Cannot be created
Batteries are used as ammo for carbine.
trade cost: 10 Scales
production by armourer cost: 1 steel + 1 sulphur (per 10 sec)