1. Basically, it wasn't fully explained what was special about that cave water; it was sort of implied to have a bit of Energon in it (which is fuel/food for Cybertronians and also their "blood") but it was also deadly to an Energon-eating monster somehow??? But the biggest hint to its importance is because it's connected to Quintus Prime somehow, one of the Original Thirteen Primes (almost treated as demigods), whose artifact the Emberstone is what created Nightshade and the other Terrans in the first place. The cave water in the caves connected to Quintus Prime and the Emberstone is what they need to survive, because they only have trace amounts of Energon in their systems even while fully "charged" and can't use Energon to refuel.

All that said, unless you something easily comes to mind for a location where recharging would make sense, I'd be happy to go with food converting into charge! It would be a startling change but I think they'd be intrigued by it.

2. Awesome >:3 Tol bord ahoy~