There is a metal strip inside that gets narrower on one side and as it gets narrower the resistance increases and once you press both sides it gets in contact with the battery terminals and current flows through. The lower the remaining battery capacity, the less the wide part of the strip heats up. Over the top is a heat activated colour strip thingy that shows how much of the strip is heated and thus approximately how much juice is left in the battery.
It actually did work reasonably well I always thought, but only if you did it just right. It was more a gimmick than a feature IMO - rarely did we keep batteries long enough to wonder if they were dead, and we usually determined it by putting them in a device.
I think it’s because many people misunderstood how to use it: you’re not supposed to jam your thumb on the sharp corner, rather just gently push on the flat end.
Huh, I haven't seen these things for many many years. And thought about them a few months ago and actually just bought a battery tester / charger. I don't think they exist in Germany?
Honestly, I've never heard of theses things until now.
I'd wager at least 50% of the 66 people who upvoted /u/amio haven't heard of it until now, either. They just upvote things because other people upvote them.
Were a thing in Italy I think in the 90s. Don't live in eu anymore but haven't seen one since.
They did work fine, it was just incredibly painful, and took a very long time to get a reading. Gee I might have just made some progress with my therapy.
If you had a better option, then use it. I've put these things into testers because they're too darn annoying. If you don't get a reading, you have no idea if the battery is just dead, or you just screwed up making these fiddly things work.
I'm not a big fan of alkaline batteries in the first place, and the rechargeable ones are great to use in medium and high drain devices that are used frequently, but for anything that's low drain or sits for a long time without being used, the batteries tend to drain themselves faster than they get used. Even if the device is completely off.
I vastly prefer any form of lithium over most of the intermediate rechargeable technologies.
I had a bad habit of touching the negative pole of a AA or AAA battery to my upper lip, and the positive to my tongue, and you can feel a bit of current and sort of gauge how much charge the battery had. One day I saw this mini battery for a camera just laying around. I did it without realizing it was an A23 12 volt camera battery. I literally saw lightning in my eyes and never did that again without making sure I wasn’t going over the usual 1.5 volt AAs.
I was installing lights once on a stepladder. Asked my girlfriend at the time, "can you switch off the fuse for the bedroom?". "Sure thing!" was the reply. I got a massive jolt that spread down my body and rattled the ladder. Somehow didn't fall. Just stepped down and processed a few things.
I've got an analogue version of that. Absolutely fucking useless it is. Every device seems to have different thresholds for acceptable levels of power.
There was a small white circle on the copper top side and a half circle on the bottom non nipple side.
What you needed to do was cover the white circle on side of battery with a thumb and then cover the whole bottom with other thumb and the indicator would tell you how much the battery had left.
Since it was a half circle off the bottom many people didn't know they were supposed to cover up the whole bottom. Making it hard for many to use it because you'd have to press down very hard on the edge to get it to work.
Or the pain of having to do percussive maintenance to get them out of tight-fitting battery compartments? I remember those constantly getting stuck in my little Mag-lite.
I've been using Ni-Mh rechargeable batteries for a lifetime now. I keep em charged, I used them for portable cameras and other devices but now they're only useful for the electric razor. Still, they save a lot of batteries that i's otherwise throw away.
My mom bought a bunch of rechargable double and triple as and a charger, and we used them my entire childhood. My friends were always in awe whenever my gameboy died and I didn't have to search through a kitchen drawer (or the freezer) for half dead batteries.