'What's a Mana Battery? Come on, don't tell me you were hired on and didn't do any research."
The woman gives you an annoyed look, as she locks the door behind her.
"Mages like us need mana in order to do the things we do, obviously." she starts, as you notice her taking up a chair. "And, one of the most readily accessible sources of mana is in semen... Or, Cum, as you degenerates might prefer. But, the higher quality the release, the higher quality the mana we can recuperate from it."
You notice her gesture you downward, as her withering glare persists.
"So, in other words, You're going to hold back your cum, until I think your release will be a good enough one to supply me with Mana."
She glances downward, with a slight sneer.
"Though, I'm not expecting you to endure much, battery."