I did an independent test 2 or more years ago, and found that out of the procell, duracell, Energizer, and energizer industrial, the regular old energizers powered a small 9v fan the longest. I tried 2 of each..
we also did a small incandescent flashlight bulb.
I have found there to be almost no difference in procells and regular duracells, or energizers, and energizer industrials.
Consumer reports showed that none of the leading battery brands outlasted any of their counterparts by any measurable amount. None lasted even 1 times as long as another premium battery.
Eveready batts have come a long way also.. I buy the 48 pack of AA's at home depot for $14, and a set of AA's lasts 3 days worth of karaoke per set. (about 18 or so hours)
In fact, if you peel open a procell, and a regular duracell, they're identical inside.
to make a battery that lasted even 1X longer, you'd have to increase the size significantly. Battery technology is such that they can pretty much pack every last bit of power into a battery now. No one has a significant advantage over any other.