I once bought a bunch of BJ's (food warehouse) branded batteries. Some leaked after they'd been on the shelf for a while, but in some packages all of them would lose voltage in a pretty short time. (Like a whole package of 9V batteries, all useless). That should not happen with alkaline batteries.
So I vowed never to buy the BJ's branded batteries again, and paid the higher amount for packs of Duracell batteries (40+ cents per AA with coupon), thinking "brand name, never had trouble with them before"). But... the duracell batteries don't like something about my cool basment, where I store them. (You'd think cool would be good, no?) So most of the pack started leaking shortly after they'd been in the basement. These batteries have a "use-by" date of 2028. I tried to get BJ's to take the Duracells back, but they said they couldn't accept them... "because of the pandemic". What utter BS.
Anyway, guess I'll try Ray-o-vac next, which I've had a lot of sitting on the shelf, but not long enough to be conclusive. But I also look for value, some of these batteries are really expensive at HD and other sources.
On your LED flashlight, yeah, they're great. They _do_ get dim as the batteries lose voltage, sometimes so slowly that you don't notice until one night you'll be wondering why you can't see anything in the light.
On top of the advice of using a little vinegar to remove the alkaline battery leak stuff, I use a sandpaper roll on my Dremel (or cheaper equivalent) tool and just shine up the battery contacts in the device if they've had some battery acid on them. It has to be a pretty nasty leak in a hard to reach spot for me to give up on my devices.