Do boss chests require Prime Energy?

The gate sits on the claim, not on the kill. You can put the boss down and still walk away with nothing if your Prime Energy is gone, because the chest and the drop materials both come out of the same daily pool. Treat a boss run as two separate decisions: whether you can beat it, and whether you can afford to open what it leaves behind.

Prime Energy refills on its own at one point every six minutes. That works out to 10 an hour and 240 across a full day, which is the real ceiling on how many boss rewards you collect. Nothing about the fight itself changes that number, so the planning question is which chests are worth spending on rather than how many bosses you can find.

The payout side has moved in your favour. Legendary stardust yields and drop rewards have been increased, so each claim you do pay for returns more than it used to.

Which chests draw on the pool

Omega boss rewards cost Prime Energy. So does the rare chest an Alpha Aniimo drops, which catches people out, since that one arrives outside a normal boss encounter and still bills you the same way. Boss chests in Holo Battle challenge mode are covered too, where the cost appears under the name Primegy. It is the same resource and the same pool, just labelled differently depending on where you are standing.

Running bosses with other players

Boss challenge events support matchmaking for teams of up to four, and they can be attempted as a duo. Extra players make the fight itself easier to finish, but the claim at the end is still an energy expense on your side. Grouping up is a way to clear more bosses in the time you have, not a way to open more chests than your daily recharge allows.

Not settled: How much Prime Energy a single boss chest takes is not settled, and the cost may differ between Omega bosses, Alpha drops and Holo Battle. The recharge rate is the firm number.