Source: Player's Guide to Faerûn
Your can store more spellfire energy levels than normal.
Prerequisite: Concentration 20 ranks, Endurance, Spellfire Wielder.
Benefit: For the purpose of determining your limit of stored spellfire energy levels, treat your Constitution score as if it were 4 points higher than it is.
Special: You can select Epic Spellfire Wielder multiple times. Each time you take this feat, your limit of stored spellfire energy levels increases by 4.
Normal: Without this feat, a spellfire wielder's limit of stored spellfire energy levels is equal to her constitution score.