GURPS Powers introduced Energy Reserve. It costs [3] per point and functions like FP, but with the following modifications:
- It must be linked to some Power source - so it needs to be Magical, Psionic, Biological, etc, and only abilities of the same source can use it (so you can't use ER (Psionic) to cast spells, or ER (Magical) to use psionic powers).
- It recovers at a rate of 1 ER per 10 minutes, regardless of activity, rest, Advantages such as Fit, etc. ER (Magical) does benefit from the Recover Energy "spell," however.
- It cannot be reduced below 0.
- There are no penalties for being below 1/3 of your maximum ER - a mage who has expended all of his or her ER (Magical) simply no longer has the ability to draw on it for casting spells until (some of) it has recovered.
- It can be used to pay both for powering abilities/skills with a built-in FP cost, as well as using Extra Effort and Stunts with those abilities/skills, but not for normal use of Extra Effort (or other normal uses for FP, like running).
There are further modifications you can make to ER, such as only recovering under certain conditions, recovering more slowly, not working for Extra Effort/Power Stunts (or
only working for such), etc. If you wish to give mage characters some free amount of it based on their IQ and/or Magery, you can certainly do so as GM - but note that's arguably a bit unfair to players who are playing non-mages who have high IQ, which - unless you give the option for them to get points back for not having this free ER - might result in anyone who opts to make a high-IQ character going ahead and making them a mage while they're at it so they get full use out of their points.