Unexpected cell polarity.

Conventional dry cells used a zinc shell negative and a central carbon-rod positive electrode. Alkaline cells are inverted: they use a steel shell positive with a powdered zinc negative surrounding a steel spike current collector. To conform the the old physical standard, alkaline cells are usually made with a nub on the steel shell and a flat plate on the spike. When used inside a 9-volt battery there is no need for that.

I'd have to say my biggest polarity surprise was finding out that 9 volt power supplies for instrument effect pedals are reversed from the standard (center positive) barrel plugs. I thought I'd lost my mind also when I didn't notice the minus sign on my volt meter. I was told it had to do with plugs that disconnect batteries when inserted. Can't imagine why

Jim

I found this to be true of many AA cells I took apart as a kid. Once I removed the outside, I found the dimple was a separate cap on the smooth bottom of a can. So the outside of actual body of the cell was positive and only the tip on its cap was negative. It was then wrapped in paper/plastic that made the opposite appear true.

Jorg Jorgensen

Fully discharged, both plates are lead sulphate, so they will take a reverse charge, especially certain contructions. But they really don't like it!

If you want to extract AAAA's, get the 9V batteries that have a 6LR61 label. Those labelled 6F22 have a different structure inside.

That mixed with some red carbonated wine, could cause mass korn fusion. 🤣

Good to know.

last week I opened an old laptop battery and found 4 of the 6 18650 cells reversed polarity. At first I thought I was losing it.

Aaron Nadler

Tricky, tricky manufacturers!

09Klr650

It's not something you'd even check - the guy I work with has been a vehicle electrician for 30 years and he'd never seen it before either ;0 Always been paranoid about connecting things the right way (too many vehicles with red wires on the -ve side) - now extra paranoid!!

I had that happen to some very expensive "house" batteries on a bomb disposal truck many years ago. It did some evil things to a few VSR's until I realised they were reversed!

Speaking of polarity - I recently tried to use a "waiting for recycling" car battery to test some equipment but my test probe failed to work when connected. On closer observation, the battery had actually swapped polarity! I was gobsmacked but the Internet tells me this will happen to lead-acid batteries if they're deeply discharged = apparently Certainly explains why the car was behaving VERY oddly ;0

I opened a dead 9v battery and the cells inside had the polarity marked on them

Jonathan Brown

I would've made an incorrect assumption.