[Anaraxes]

So, you want a Limitation that imposes a restriction of how many points you can spend out of your ER per turn. (Or other time unit, perhaps; the fact that you can only take one Maneuver per turn limits you to using one ability at a time anyway.)

The GURPS ER is really a buffer that lets you burst activity. Long-term rate of ER usage is equal to the rate at which the ER recharges. So, one way to build in a rate is simply to use a small ER, but have fast Regeneration. Using an ability drains the ER; the Regen builds it back up at the end of the turn.

The size of the ER pool in the other game (if I understand correctly) is then the total amount of energy you can spend in one combat, scene, etc. (There's probably some relatively slow recharge time that resets the ER pool mechanic.) If you want to simulate this kind of maximum combat endurance, you might put Maximum Duration or Limited Use on the Regeneration. If you can only Regen for 5 seconds before losing the ability to Regen, then you can draw from your small ER for only five seconds before it runs dry.

You could, of course, just invent a brand new Limitation and define the way that it works.