Mana Batteries

[Alex Koponen]

One of the nicer little items a spellcaster can find or make for
themselves is a Mana Storage Item, often called a Mana Battery. (Often
placed in their Staff). What is REALLY nice is that Mana Batteries
automatically recharge themselves completely in 10 days.
  Listed under Optional Ensorcellments, no maximum is mentioned for the
number of Mana Batteries a spellcaster can create and/or use. I can readily
imagine a spellcaster having dozens of Mana Batteries and thus being able
to average many times the number of spells per day than they could
otherwise.
  Basically I think it is flawed.
  Possible solutions I've thought of are:
- Allow a maximum of (EL in Ensorcelment) ELs of Mana Battery. Oh, and
don't lose it as you can't replace it as long as it still exists. Maybe
allow ELx2 if the Mana Battery is Dedicated. [Of course what happens to the
Mana Battery after the spellcaster dies? Does someone else get to use it?
Eventually might someone amass a huge collection of them?]
- Allow any number of Mana Batteries, but they don't recharge except by a
spellcaster transfering Mana into it from Casting Ability. [My preferred
solution.] One could even be nasty and put some inefficiency into them so
that for each X Mana put in only Y Mana can be brought out and used.

Any other suggestions? Comments?