Could the order of batteries in a device affect their relative depletion?

[Woodface]

[FONT=verdana, arial, tahoma, calibri, geneva, sans-serif]In decades of using ordinary domestic AA, AAA, C & D cells, I have been intrigued by why some seem to fade a little faster than their supposedly identical siblings from the same batch. When used together[/FONT] in series in[FONT=verdana, arial, tahoma, calibri, geneva, sans-serif] a device in pairs, threes, fours etc. The curiosity persisted as I went on to use and mend rechargeables and multi-cell power packs found in powertools etc. [/FONT]

Logic suggests it's just that not all batteries are created (100%) equal. But I always had a vague suspicion that just maybe the position of a cell in the circuit might have some effect on which loses charge fastest or slowest.

Picturing the old doubtless unscientific analogy of electrons flowing round a circuit like water round a heating system, I wondered if being closest to the 'flow' or the 'return' might see the cells stressed in a slightly different way from each other.

Is it conceivable that being closer to (or furthest away from) the load would affect anything? [FONT=verdana, arial, tahoma, calibri, geneva, sans-serif]
[/FONT]
[FONT=verdana, arial, tahoma, calibri, geneva, sans-serif]Has anyone else noticed any pattern based on placement? (I spent a lot of time fruitlessly googling for anyone else talking about this. And Google tends to have extensive results of people writing about every daft idea under the sun.)[/FONT][FONT=verdana, arial, tahoma, calibri, geneva, sans-serif]
[/FONT]

[FONT=verdana, arial, tahoma, calibri, geneva, sans-serif]Has anyone ever tried marking their cells and recording any pattern over time to see if position in the battery bay makes the remotest difference? (I guess I should have since it's my crackpot conjecture). [/FONT]
[FONT=verdana, arial, tahoma, calibri, geneva, sans-serif]
[/FONT]
[FONT=verdana, arial, tahoma, calibri, geneva, sans-serif]I'm sure replies will lean to the negative. But I'll try to stay positive [/FONT]
[FONT=verdana, arial, tahoma, calibri, geneva, sans-serif]
[/FONT]

 

[archimedes]

Hello and welcome to CPF .... Your post above has been approved.

This finding has been noted and discussed on CPF before, so I wouldn't call it a "crackpot" idea.

Of the many possible (and likely) contributing factors, the effects of heat would be at the top of my list.

 

[LED Monkey]

As heat was just mentioned, I did watch a video of a Tesla car dismantled battery pack where the cells were tested for capacity, and the cells that were exposed to the highest heat levels consistently show a slightly lower capacity. That being said I did have some nimh batteries in series in some Christmas decorations, all brand new batteries and when I would charge them I did notice that at least 1 out of 3 would show a lower discharge then the others. In this case I would say heat (at least to me) did not seem like a factor because the batteries would always feel cool to the touch and were not close to the light source in the battery pack. I did even do a charge/discharge cycle to check if the batteries were even in capacity and I did have the batteries show 1 cycle of all three batteries showing the exact same mah, down to the 1/100th of a volt. Which was pretty impressive. Eneloop btw.

 

[ben65]

From an electrical point of view, cells in series experience exactly the same electrical conditions. I.e., there is absolutely zero difference between the cells "closer" or "farther" away from the load.

The only seemingly electrical difference I can imagine is a difference in the resistances of the electrical contacts along the series. Imagine an extreme case where one of the contacts is really bad with very high resistance. This will cause local heat at that contact that may affect only one (or two) adjacent cells. Note, however, that from an electrical point of view even in this case all cells experience exactly the same electrical conditions since this contact resistance is in series with all the cells. It is the thermal conditions that are different!

However, this is no longer true in case there are center taps, i.e.,connections going to the middle of the series of cells, and not only the two connections at the positive and negative ends. That said, center taps are extremely rare in most products, and certainly flashlights. An exception are li-Ion battery packs where the charging balancing circuit has wires going to each individual cell(s) in the series arrangement. In this case asymmetry in the balancing circuit may treat individual cells differently and thus contribute to differences in their capacity and lifetime. Remember though that this pertains to battery packs and not individually fed AA, AAA, C & D cells.

To summarize, individually fed AA, AAA, C & D cells almost always have only two end connections, which means that the in-circuit electrical conditions they are under are completely independent of their order. Differences in lifetime and capacity are thus attributable to chance or non-electrical physical conditions (such as proximity to heat from other components, heat dissipation paths, etc.) which in certain instruments may indeed depend on the position of the cell.