How do those integrated battery testers work and how reliable are they?

I mean the kind of batteries where, if you push down on two spots on the cell’s wrapping, a small bar fills in proportion to how much charge is left?

I assume it’s some sort of chemical reaction, but what chemicals do they use and how does it test the battery. Is it even accurate?

it is a resistance path next to a liquid crystal with image underneath. pushing the spot allows some current to flow generating heat which causes the liquid crystal to become transparent and show the image underneath in a proportional fashion.

Do they even still have those? I haven’t seen them on a battery in years. I liked having them, even back when they were just part of the packaging, but right on the battery, that was so convenient.

They seemed to disappear for a few years before I noticed they were selling batteries with them again (it’s the difference between Duracell Plus and Duracell Ultra, apparently. In the UK at least). That’s what prompted this topic.

Sorry to double post, but is it possible to remove the strip from the battery? Could it be cut down to a smaller size and used for something else?

I just realised that if that’s the case there’s all sorts of projects I could use it for.

Yes, it can be removed. The ham radio magazine QST (I think it was) published a short article on using them as an RF ampmeter a few years back.

Oh, you’re in the UK. Maybe that’s why I haven’t seen them.

I don’t suppose there’s an online version of the article somewhere you could direct me to?