19 Oct 2005 at 15:57 - 3
Exhaustion causes a decreased energy regen once the energy bar reaches the new, lower cap, so in effect a spell with exhaustion uses more energy per time. To answer the question, though, I'd say it basically amounts to about a -1 energy regen for some period every so often, depending on how you are fighting.
If you are stopping after every battle with the opportunity to fully regen, then exhaustion has little to no effect. If you are involved in long drawn-out battles then it can be a factor. Now if you're a Mez primary echo-nuker, I would imagine exhaustion would be a huge problem.
I find the solution to all energy problems with ele's is energy management, though. If exhaustion is hurting you, you probably need another way to keep the mana flowing anyway. There's the enchantment (forget what it is) that does the 30% energy cost reduction, which is nice, and Necro and Mez have many energy-boosting skills.