Failure of a C cell in a 4x battery pack, potential causes?

Question

I am trying to understand failure of cells in battery packs of 4 x alkaline C cells (in series, so ~6V output). The failed cells, from 2 separate battery packs, have bulged and leaked out, you can see the photo below:

Unfortunately I didn't get a chance to see the battery pack as whole unit before I started investigating but I've been told that at least 1 cell (not clear if it is the affected one) might have been placed in reverse polarity in the battery pack.
Would I be right in thinking that given that a cell might have been placed in reverse polarity, it is possible perhaps that somehow other batteries around it (with more charge than the affected one, possibly) could have caused a "reverse flow" of sorts and heated up the cell to the point that it vented out its innards?
These battery packs were assembled on the factory floor so it is also likely that some of them were dropped on concrete floors before they went in the packs, seems unlikely but do you reckon the combination of the reverse polarity plus potential damage from a fall could have contributed to the failure?
Difficult to get to the bottom of this with unknowns but I guess the jist of it is: Can a reverse polarity cell, in a series arrangement, be damaged by other cells around it?

Jasen · Answer

Backwards could cause it, but it can also just happen. I had one cell from a pack of four loose voltage well before the others. this triggered an alarm so replaced them all. If I had continued with them it could have reverse charged the weak cell and caused a leak. after a second duracell destroyed my maglite I stopped using that brand.

Answered by Jasen on December 19, 2021

Kyle B · Answer

A reverse-inserted cell in a series chain of cells effectively is being charged by the other cells.
And it says very clearly on the battery "Do not charge - may leak or explode"  ;)
Take a look inside a young-age-grade toy's battery box and you'll find there's extra plastic or battery contacts added specifically to make it impossible to reverse-insert a cell, thus preventing parents from burning their kids this way.

Chris Stratton · Answer

Difficult to get to the bottom of this with unknowns but I guess the jist of it is: Can a reverse polarity cell, in a series arrangement, be damaged by other cells around it?

Most definitely if there is a load which will pass more than trivial current completing the circuit.
Consider something simple like a 4-cell flashlight.  You basically have 4 cells in series with a small resistor.
But if you turn one of the cells around, now you have three cells trying to charge one cell through a small resistor.  Given the high voltage and the low resistance, this will probably exceed the charging limits... especially for a cell that is not designed to be rechargeable to begin with.
But that doesn't mean you can rule out other damage mechanisms.
Or fakes.

Failure of a C cell in a 4x battery pack, potential causes?

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