I have a unproven suspicion that Rechargeable Energizer may actually be Panasonic cells. I tend to see them both marked as made in Japan and they both seem to be great quality.
Could be. I have no special insight into Energizer, but generally, the private-label product you buy today might not be the same six months from now. And even if they are Panasonic cells, they might not be identical to Eneloop, either.
The private-label guessing game cuts both ways, too: there are 2nd-tier alkaline manufacturers that swear they are a contract manufacturer for at least one of the major US brand names, with portions of their factory they can't show you because then you'd find out. Even if it's true, it doesn't mean the battery they sell you will be built to the same standards, with the same materials, or put through the same QA as the battery they make for someone in the battery business.
The private-label guessing game cuts both ways, too: there are 2nd-tier alkaline manufacturers that swear they are a contract manufacturer for at least one of the major US brand names, with portions of their factory they can't show you because then you'd find out. Even if it's true, it doesn't mean the battery they sell you will be built to the same standards, with the same materials, or put through the same QA as the battery they make for someone in the battery business.