Where did the battery "rotation" idea come from in dual battery mods?

[Confuzzled1969]

OK, I have been reading on here on one thread after another that batteries should be "rotated", or on one use it should be the top battery and on the next use it should be put in the bottom, or left vs right.

Where does this come from?

What difference does it make?

I can't find anything that describes the "why" of this reasoning.

All the rest of the pre-cautions, same batteries together all the time and such I totally agree with, and there is literature to support it, but this one baffles me, and so far I have found no information anywhere except in relation to e-cigarettes.

I am very familiar with battery systems and back-up battery banks, I deal with them professionally.

I maintain over 80 large UPS systems (50 - 75 KVA) that use a string of either 30 or 40 series connected high discharge batteries, and they are never rotated. They sit stationary in the same spot unitl they fail and they are replaced.

Does anyone have any solid information on this?

 

[roosterado]

In a side by side Dual Battery Mod like my Dual 26500 VV Beast Box-3.3 to 8 volt the theory is 1 of the battery placement gets stressed more Thus over time You end up with not quite a matched set of batteries.

 

[Confuzzled1969]

In a side by side Dual Battery Mod like my Dual 26500 VV Beast Box-3.3 to 8 volt the theory is 1 of the battery placement gets stressed more Thus over time You end up with not quite a matched set of batteries.

I can find no evidence to support said theory.

But at worst and best it seems to be the same as cracking ones knuckles, completely harmless unless it offends someone...

I was just looking to find something more tangible to it...

 

[Ryedan]

The conventional wisdom is that when batteries are connected in series the one closer to the load depletes a bit faster than the other battery. The good thing is that we generally charge our batteries outside the mod and each is brought back up to full charge every time. In built in multi cell battery packs there is a charge balancing system used that makes sure each cell is brought to full charge every time. I would think that in more expensive and more mission critical battery packs the charge status of each cell would be monitored through discharge, but that's just my opinion. I don't know that this is important for parallel cells.

If you continually discharge one cell more than the other that cell is going to become weaker (higher internal resistance) and will eventually become quite stressed at the end of discharge.

I just did a few Google searches and did not find anything to back this up. Hopefully someone who knows more about this will help us both out. If you do more work on this yourself, please let us know what you find out

 

[AzPlumber]

I would think any precaution taken is a prudent one when using such power right in front of your face.

 

[edyle]

OK, I have been reading on here on one thread after another that batteries should be "rotated", or on one use it should be the top battery and on the next use it should be put in the bottom, or left vs right.

Where does this come from?

What difference does it make?

I can't find anything that describes the "why" of this reasoning.

All the rest of the pre-cautions, same batteries together all the time and such I totally agree with, and there is literature to support it, but this one baffles me, and so far I have found no information anywhere except in relation to e-cigarettes.

I am very familiar with battery systems and back-up battery banks, I deal with them professionally.

I maintain over 80 large UPS systems (50 - 75 KVA) that use a string of either 30 or 40 series connected high discharge batteries, and they are never rotated. They sit stationary in the same spot unitl they fail and they are replaced.

Does anyone have any solid information on this?

The difference I think is whether you're series or parallel.


With series, when batteries are not balanced, things go south faster.

So to answer your question: It matters whether you're talking
1: "top battery and on the next use it should be put in the bottom" - which would be in series usually
or
2: "left vs right" - which could be in parallel, but could also be in series.

 

[Stosh]

The practice of rotating your batteries in your mod go back to stacking low drain batteries (old Li-ion ICR protected) in mech mods, using 3-4Ω atomizers. It was observed in testing the voltages on the batteries after use, prior to charging that the voltage levels were not near equal. The "top" battery was always lower, rotating the batteries was done to attempt to keep the aging of the set equalized. This was a result of measuring the battery voltages, not recommendations of battery engineers, the technology was cruder.

With modern high drain IMR and hybrid cells in modern mods, it would have to be tested and measured again to see if the differences still exist. Differences in the aging and internal resistance of your batteries could add extra stress to batteries that many are pushing to their published specifications regularly. Not sure how many vapers still check the battery voltages of their sets every time prior to charging.

With on-board charging I would still want to check my voltages to be sure one cell isn't being stressed and aged faster than the other, it's my OCD, and I like my ugly mug just like it is presently....

 

[Silver5656]

I asked a similar question to this as well, and got no definitive answers w/o doing more research. Read the last couple posts in my thread.

http://www.e-cigarette-forum.com/fo...eries-parallel-battery-marriage-question.html

 

[Froth]

Not sure if it has anything to do with being in pairs but the only battery failure I've had thus far was one of my LG18650 HE2's that I used in a pair since new in my bottom feed box mod, I never kept track of which battery was in which position and eventually I think that had something to do with one of the cells no longer holding a charge. I was pretty adamant on checking the voltage of each cell when I removed them to charge and there was usually no more than a .1 or .2v difference between the two, I generally saw ~3.4 to ~3.6v when I needed to charge them after removal. About six months into using the batteries I was noticing some well below par performance, pulled the batteries and one of them measured 1.09v, tried to wake it back up in my Xtar charger, no dice. Not sure it had anything to do with pairs being rotated, but it did happen. The other battery of that pair is still working to this day.

 

[Silver5656]

Lithium-Ion Battery Cell Balancing

this could be an explanation regarding the dead batt

This is also the reason why I will never charge dual batt mods using the usb, either in series or parallel

 

[Ryedan]

I asked a similar question to this as well, and got no definitive answers w/o doing more research. Read the last couple posts in my thread.

http://www.e-cigarette-forum.com/fo...eries-parallel-battery-marriage-question.html

Your link in post #11 is a great reference for Li-po and much of it applies to most Li-ion. The one on cell balancing a few posts later is good in that it explains how cells in a pack will become unbalanced over time. The example of balancing a series pack by completing individual cell discharge is not how it works with charge balancing boards today obviously, because they don't discharge. It's done at the other end, by completing the charge for the slower cells. I know there are Li-po battery packs that have cells in parallel and combinations of series and parallel, so there is a way to balance them too.

I have the feeling that it's not critical to swap series cell positions these days when putting back batteries. If we always put the same cell in the same spot, over a few hundred cycles one may become significantly weaker than the other. However even if we put them back randomly, they would get rotated pretty well over that many cycles. I know I would rotate anyway, but that's just me

 

[Ryedan]

Not sure if it has anything to do with being in pairs but the only battery failure I've had thus far was one of my LG18650 HE2's that I used in a pair since new in my bottom feed box mod, I never kept track of which battery was in which position and eventually I think that had something to do with one of the cells no longer holding a charge. I was pretty adamant on checking the voltage of each cell when I removed them to charge and there was usually no more than a .1 or .2v difference between the two, I generally saw ~3.4 to ~3.6v when I needed to charge them after removal. About six months into using the batteries I was noticing some well below par performance, pulled the batteries and one of them measured 1.09v, tried to wake it back up in my Xtar charger, no dice. Not sure it had anything to do with pairs being rotated, but it did happen. The other battery of that pair is still working to this day.

That's interesting Froth. Do you remember if the voltage discrepancy got worse before that one died?

 

[glycerol]

On my V8 (2x 18350 in series) I notice that one of the cells always takes like 2 minutes longer to fully charge, but I never cared remembering which one and I let the fate decide which one goes where. I think, as long as a *regulated* mod is concerned, pairing is enough. I wouldn't use a dual-cell mech, though - not brave enogh to even use something bigger than a 18350 lol

 

[hazarada]

Hogwash, when connected in series, the order makes no difference in degradation whatsoever. Yes there are mechanisms in play that cause the different batteries to degrade at different rates but one of these mechanisms rules over the others by far: in case of lithium-ion, the battery with the shortest cycle (the most degraded) gets stressed the least during discharge. This will at first equalize the battery R/C and then keep it there no matter what order they come in.

Also its totally fine to charge the batteries in series if the completing circuit is built with that in mind (and in case of high current batteries, even without). If theres no special logic in the closing circuit, the battery with less charge will leech off the one with more charge, eventually equalizing them during use. If the closing circuit is clever though, it will limit the current in case of a big differential to prevent the less charged battery from overheating. Or if extra clever, it will drip current during periods of inactivity to speed up the process safely.