This is the forum for helping you out if you're stuck or if you want to discuss the nitty gritty details of the dungeons within Mount Grimrock. Warning: forum contains spoilers!
I dont think it recharges (i've already used all it's charges in a challenge... then gave it to my lizard rogue for safekeeping) good news is.. it doesnt just turns into a "dull old longsword" after the charges are spent... it still deals fire damage... but i've still yet to see if enemies are susceptible to specific kind of damage... not enough tests
note: it deals fire MELEE damage, as opposed to the fireball it shoots when charged. The same thing happens with a poisonous dagger you find a few levels before... forgot where.