Magic Item: Power Cord
This item presents as a finely woven decorative cord, as may be seen around the neck of a priest or academic character. These cords come in various colors and patterns.
When 'empty' the cord radiates a faint magical aura for those detecting magic. The cord can be charged with magical power, however, either by the Meditate skill (Warhammer) or Spellcraft nonweapon proficiency (D&D) or the like (for whatever system you use). The cord is charged as per the Meditate skill (Warhammer) or 1 spell level per hour (D&D). Charging the cord means that the spellcaster's own personal magic stores are not regenerated, so the caster must wisely decide if he needs the power or if it can be stored.
Stored magical energy can be used for casting spells, like a Jewel of Power (Warhammer) or Rod of Spellcasting (D&D). When desired by the caster, the spell energy is utilized from the cord instead and the caster retains all their own spell energies.