improving "duff" batteries ?

i've been stripping old laptop batteries to reclaim cells and testing them for capacity.

I boost charged a number of "dead" cells up to the point where a lithium ion charger would "see" them and charge them properly.

Afterwards I sorted them out, dumping some that were beyond hope, kept the good ones and also put to one side a bunch of low capacity cells e.g 1000-1400 mah thinking I could maybe use them for other projects such as torch batteries etc.


I've just revisited this pile and I decided to retest a couple of cells where I wasn't 100% clear on their original capacity becuase the sharpie had smeared on them

They both came out around 500mah more than what I thought was written on them. So I started retesting more of my low capacity cells and a lot( but not all ) were also giving significant increases over the original capacity testing.

Is this normal that is so called "dead" cell will actually need a few cycles to bring it back up to its full potential capacity ?

It depends on the charger you tested with. All does it differently. Yes some may show more on 2nd time but in generall lithium does not have memory affect. But with that said somepeople tend to see an increas of capacity on 2nd attempt on cells that had been dead for some time.

daromer said:

It depends on the charger you tested with.

Click to expand...

Both times around i tested withthe same equipment. A Turnigy Accucell 6.

the only difference was the first time around i charged solely with the Accucell before discharging and marking them up

i then recharged them up in a rig of TP4056 boards and battery holders i made up, before putting them into storage.

when i came to test them the second time i topped them up with the accucell before dischargeas a quick test but it really was not needed as the Accucell put no more than a few Ma in before reporting them full. i then switched to discharge mode and re labeled them with the new capacity. ( i then recharged them again in the TP4056 rig)

It's also possible that, depending on which cells and chemistry it was built on, that the oxidation layer, if it had one to begin with, hadn't fully burned off in the first charge. After letting it sit with full charge in them, it allowed that layer to finish burning off. The oxidation layer, if it had one, is a barrier of resistance, which changes the mAh rating. So, after it burned off, the resistance dropped during the second charge, and you got a higher mAh rating.

This, is of course, speculative, hypothetical, guesswork. Who knows really why in the end? The important thing is, you have more mAh than you thought you had, and that's always a good thing!
It would be interesting to test this over time to see what effect it has.

Without speculating what the exact reason is, lithium cells that are new or used ones that haven't been used for a while might need some cycles before reaching their maximum capacity (again). So this is normal for all lithium cells, not necessarily only the dead ones.

This isn't normal for lithium ion cells, but perfectly normal for pure lithium cells.

i know it's been a long time since i posted on here but i now know what was causing the difference and that was the Turnigy charger's profile on Li-ion setting only charges to 4.1V
whereas when i was charging with TP4056 it taking them to 4.2V.

i was getting different capacity readings during discharge depending on what i had charged with initially.

if instead you select to Li-poly setting on the Turnigy Accucell charger it will take the cell(s) to 4.2v before cutoff.

thought i'd post it in case anyone runs into same issue in the future