As the creator of Mana Batteries, Aegon knew everything about them, so he quickly understood Samuel's confusion. After all, they hadn't used any external source of mana like they intended to do with the factories.
"Quite simple," Aegon answered. "I have engraved Mana Gathering Formations into it too, so the mana is just taken from the surroundings. It'll work for now."
Samuel nodded in understanding.
This wasn't a plausible long-term solution, as the rate at which the Mana Batteries were produced would drain the surrounding mana in no time, and it took time for the environment to fill those gaps again.
The world had infinite Essence, but it was spread everywhere and existed in many forms, so this imbalance happened whenever someone extracted it too rapidly.
The only reason nobody noticed was because the mansion had a giant Mana Gathering Formation, so the interior held mana in far greater quantity compared to outside.
