Firebolt is the staple spell of all mages and the first Battle Magic spell that the PC learns. It costs only 4 Spell Energy while consuming no essence. This allows it to be relied upon as a mage's default attack with little need to monitor resource consumption. Firebolt, as the name suggests, deals Fire Damage in Geneforge 4 and 5.
The energy requirement is so low that many beginner players have their spell energy recharge at the same or greater rate than what is used in a single cast.