The Zarth use two types of batteries, mechanical, and rth. The types can be cross-converted, but generally with large losses.
Zarth have access to metals which allow them to make super-powered springs. They store energy from their various energines for use in weapons and spells. These can be very small and simple (pocket-watch sized) up to huge wagons with built in gearing.
Most zarth would probably wear a small standardized battery around their neck, in pendant form, for utility purposes. Gear batteries could also be included in jewelry (Powered jewelry? Yes!).
The larger batteries would be used to power vehicles and some hand tools. Stationary tools and machines could have their own energines attached.
If a battery breaks, the energy stored would (probably) be released very quickly, resulting in an explosion. This property could be employed to create grenades and mechanically explosive projectiles (no chemical explosives needed). Since the energy is stored intrinsically, a very high energy battery would be dangerous to handle, and difficult to disassemble without safely discharging first. Discharge and conversion energines would probably be used for just this purpose, especially where batteries are serviced and repaired.
Most batteries can be wound with energines.
Wielding consumes the life energy of Zarth, called "rth", reducing their lifespan. Rth can be transferred between Zarth, or used to create new Zarth. Various substances have varying responses to rth. The form and abilities of a Zarth is largely based on the stone from which its body is carved.
Rthium is a naturally occurring crystal which has a high capacity for storing Rth with very little loss to conversion or leakage over time. For this reason, it is almost universally used to transfer Rth between Zarth, instead of direct transfer. An Rthium crystal used in this way is also termed a "battery".
Because Zarth have a minimum amount of rth required to stay alive. However, too much rth can make a Zarth sick, or even kill him. For this reason, only very wealthy Zarth carry charged Rthium on their persons. When they do so, it may be in the form of jewelry or other conspicuous displays of wealth and potential longevity.
Batteries can be combined for convenience. These combined batteries take a variety of forms, sometimes a large shard of Rthium surrounded by a ring of gears, or a gear studded with Rthium.
Charged batteries are part of the Zarth tax. Each citizen has to supply a certain quantity of strength, for the defense of the borders, building of infrastructure, etc. This can be of either type, though usually a combined battery of a specified design is required for consistency. Since magical effort translates into shortened lifetimes, this is an actual tax on life!