I purchased a flashlight that came with 3x AAA cells. These are branded with the flashlight brand, labeled as Alkaline (Mercury and Cadmium free), LR03 AM4. Made in China. I am dubious of the Alkaline claim, but at least it's not a "Heavy Duty" cell.
What's odd is that the flashlight was working well, at full brightness. Then it dimmed. Some percussive adjustment it went back to normal, but eventually back to dimmed. Opened the flashlight, checked for corrosion, leakage/vented or a bad connection, there is none. Moved the batteries around, and suddenly back to normal. The slightest movement cause it to go back down.
Eventually I identified one of the cells as the issue. I could rotate it in place, and at some point it would work. This was the odd part. I couldn't get it to work normally again. Worse, I measured the battery voltage. -0.3V. Somehow, it has reversed it's polarity? A second set of these batteries from another flashlight shows one of three also having the same issue. -0.1V, while the other two show 1.49 and 1.52 volts. When on, this bad cell jumps to -0.56V when the circuit is pulling 5mA.
Obviously, this is a bad battery of questionable quality, but this is the first I've seen a battery go bad like this. What would allow a battery to fail and reverse itself? A normal chemical process? The other two higher voltage cells attempting to charge into a lower voltage cell (all in series)?