I had debated on having magic using characters, be it mage, cleric or bard, have a End Reserve.
All spells would have to come from them and they could only recover in a Mana area. I have several spots in my world that are mana dead.
I have since decide that Spells work of any mana not just those the caster has. So as long as the spell is being cast in a Mana area it will work.
The caster spends end to show the strain f casting a spell.
Items with out charges work the same way.
Your +2 sword is only +2 in a mana area. Healing potions that have 4 charges however are different. Weapons are designed to use the mana in the area to work. Potions and such have the mana put into them when their made. The won't go away until the mana is used up.
Now anti-magic shells will prevent them from working, being a surpression, but a mana dead area will do nothing to the item.