Monsters gain and use mana the same way the player does.
Feeding them a mana potion should allow them to use their abilities right away, and also increase their maximum mana capacity.
But they still gain mana at the same rate as before drinking the potion.
Thank you for the reply!
I did start to notice that they do tend to have more usage of their flame attack more often since upgrading their mana.
It would be nice to have an Npc(s) mana to be listed in their examine window with the rest of their stats.
P.s. I have a selfish suggestion. If there is ever a way for a summoned ally to retain their inventory. That would be a godsend. I tested giving a blessed +30 iron dagger to one of the two viper summons. However upon resummoning it lost both the dagger (and a ring). It does limit the book of summoning a bit.