Sharing energy was a mental power that involved two magicians or dragons linking their minds. Whenever one of them would use magic, the energy cost would be split between them.
Description[]
The magicians and/or dragons would link their minds before sharing energy. There weren't any visible effects.
Uses[]
Sharing energy was a very useful tactic for Dragon Riders, especially human Dragon Riders. Because dragons had more physical strength and energy than humans or elves, they could easily withstand the loss. Divided, the energy between them effectively doubled what a spellcaster was capable of, making them much more powerful.
Role in the books[]
Eragon and his dragon, Saphira, would join minds whenever one of them was in danger, so they would be more powerful then they were alone. Some situations where this happened include healing Brom, confronting the Twins, thwarting Murtagh's scrying spell and trying to break Murtagh's restraining spells.
Arya and a group of supporting elves shared energy with Eragon and possibly Saphira during their battle with Murtagh and Thorn in Brisingr.