[reb]

i use power stones as sort of a 'battery' in a sense,and they can be recharged by any mage who knows how to channel energy.

some of the items in my world have specific runes and ways that must be known by the owners to be able to activate them or 'unlock' them,thus enabling their use.
in my games 'power stones' are a called mage crystals and are a naturally occuring mineral/crystal which can be found in certain places and there are different types.
these crystals have the natural ability to 'absorb' and draw ambient energy from their surroundings.
they are usually very potent and give off radiation and must be worked to use them and slivers are used in staves and other devices to power them.

a staff or some other items can be simply 'stuck' into the ground and they will self charge over a given time.
the better the mage tech(what magic item technology is called in my world setting),the better it will draw energy more effeciantly and thus recharge faster at a faster rate.

or a energy storing device can be used to tranfer energy directly from that item/device and recharge a depleted device.

so i have developed multiple ways for a device to be recharged.

a device can be overloaded and it will explode if it's energy capacity is forcefully exceeded(not a good thing!)..kaboom!!

the better the item is made and the more sarjenium(mage stone crystal) is in the item/device the more energy it will hold.

these are just some of the basic concepts i have come up with.
maybe these will give you some ideas.....