[3.5e, Faerun] Spellfire-Powered Undead, looking for commentary and suggestions!

[Rossebay]

In our campaign, I have this character who's a 'necropolitan', but with a few changes.

First of all, Positive Energy heals him, negative damages him.

He's immune to turn/rebuke undead.

Instead, he's a spellfire wielder, and he consumes 1 point of Spellfire energy per 4 hours. Additionally, if he runs out of Spellfire levels, he is 'exhausted' for -6 Strength and Dexterity. Not the actual condition, mind you.

If one spends over 48 hours in that 'exhausted' state, they die, having used up all of their magical energy to keep them going.

Beyond that, they have all of the immunities and resistances of Undead.

Is this balanced? Any suggested changes? Should I just use Necropolitan as a base, or should there be Level Adjustment on it?

EDIT: Oh, right. They also use Charisma for everything Constitution-Based about Spellfire energy.