Battery Mystery

[Sparks]

This morning, my wife's radio stopped working, and she gave me the batteries to test. It held four Panasonic Pro Power AA cells. I tested the first three that had gone down to 1.1 Volts, but when I tested the 4th, I found it had reversed its polarity complely, and was showing 1.3 Volts with the positive end now as the negative! I wonder how this can happen?
Bob

[ppppenguin]

One cell goes flat first and is reverse charged by the others. In theory it might get hot and go nasty. This is why they say you should replace all the cells in a radio etc at the same time. Surprised it got to 1.3V reverse.

[pwdrive]

I once read, that if one battery discharges significantly below the others in a series chain then it can become reverse charged, the charge being supplied by the other batteries.

EDIT: Post crossed.

Lawrence.

[Terry]

I had a box of 100 AA Maplin branded alkaline cells about three years ago that kept doing this. Eventually I gave up and took the box plus a set of 4 that had become a 3V battery in a radio.

When they checked them, one of the staff suggested that the reverse charged cell had been manufactured with the guts put in backwards!

Eventually I got a refund for the whole box.

I now mainly buy Kodak alkaline cells from Poundland - 4 plus 2 free for a £1! The same cells are available from a number of competing outlets but you only get 4 for a pound - only Poundland, in my experience, give you six!

[Sparks]

I think that may be the answer, that they put the inside in the wrong way round to begin with. I will cehck the rest of the box!
Bob

[Terry]

I think that may be the answer, that they put the inside in the wrong way round to begin with.   I will cehck the rest of the box!
Bob

I think not!

I think it must be a physical impossibility, given where the insulation separating positive and negative is.

In any case, another instance of the same problem concerned a 3-cell wireless doorbell and I can assure you that it would not work with a 1.5V supply (1.5 + 1.5 -1.5) which is what it would have had to start off with!

[ppppenguin]

Perhaps they should deliberately make a few that are backwards. Date them April 1st

Like Terry, I don't believe it's possible to have them backwards accidentally.

[pwdrive]

The electrons feel more positive with less pressure from the voltage.......Groan.

Lawrence.

[Mike Watterson]

"When they checked them, one of the staff suggested that the reverse charged cell had been manufactured with the guts put in backwards!"

Not possible except on composite batteries such as layer cells or multiple cylindrical. Even then I can't believe it!

For Alkaline the case is connected to positive. On Zinc carbon/Chloride the case is -Ve electrode. I've had a problem with Alkaline D cells, the cover is thin plastic film easily pierced by metal chassis (invariably connected to -ve), thus shorting the cell even in single cell holders. So I print vintage 120gm or heaver labels on the laser.

I got a cheap 1.5V & 9V mechanical test meter for a few quid on eBay. It has a parallel resistance to ensure adequate load to test 1.5V cells or 9V battery. No being fooled by DVM (1M or 10M load and it needs a working battery inside!)

I found the Kodak Alkaline are OK and the Sony, Polariod or Kodak PP3 (layer or alkaline) OK. But I have found all makes of "Zinc" cells to be junk, with invariably a early leak / failure rate as high as 1 in 4 at about 1/10th of normal Zinc running time! Alkaline PP3 only worth extra for DVM and smoke alarms, the extra cost isn't covered by run time in 9V, 45V, 67V or 90V radio, only things were you need 1 year+ life.

Alkaline cells can recharge well if not discharged more than 1/3rd. (Slowly!)

[Sparks]

I can assure you that it would work with three 1.5V the correct way round and the 4th the wrong way round, simply because it did! Its performace was going down, but it was certainly still working. I still have the reversed battery, so I may open it and see if it would be possible to put the insides in the wrong way round. At the same time, if that were the case, it would be charging up, so would probably have a higher voltage than 1.3!
Bob