Battery

Concept

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.

Expansion

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 could be wound with energines.

More ideas

Mechanical batteries is a cool idea. Could we expand this to include magic batteries? A crystal which can be used to store magical energy and power spells. They could even be part of the Zarth tax, that each citizen has to supply a certain quantity of strength, for the defense of the borders, building of infrastructure, etc. Since magical effort translates into shortened lifetimes, this would be an actual tax on life!