I posted in another Pieps thread this link:
https://beaconreviews.com/recall_Ortovox_M2.php
about when a similar thing happened with the Ortovox M2. One of the offenders at that time was Kodak-branded batteries that were on the US GSA supplier list. I know "Kodak" is likely a rebranded battery, but it is a bit more reputable than random-name-Amazon-special. I have a can of half-used AA and AAA batteries on my desk (not for beacons obviously), and indeed there is some variance and Kodaks were shorter than Duracell/Energizer.
Clearly beacon makers should be aware of this shit because it has happened several times, but I also feel a little bad for the engineer who has to design for all possible shitty AA or AAA batteries that someone might buy on the internet to put in a device that needs to stay on while being tumbled like a washing machine, or worse.