Behavior of lithium cells...

[Externet]

Hi.
Noticed for multiple occasions, after recharging 18650 lithium cells individually on the same charger, after days/weeks removed from the charger, some stay at about 4.2V. Others show 3.7V.
Has anyone read any report about it ? Is it because of their chemistry, age or health ?

 

[treez]

could just be the tolerance on the different leakage current.

 

[KlausST]

Hi,

I assume you did a forum search for similar topics or an internet search...

Then you most probably already heard about


Klaus

 

[c_mitra]

after recharging 18650 lithium cells individually on the same charger, after days/weeks removed from the charger, some stay at about 4.2V. Others show 3.7V

I too had similar experiences but I did not probe further. They were all purchased together I presumed they came from the same batch. Out of 10 (bought together from aliexpress) three are unable to retain their charges.

I guess the cause is basically poor quality control. But I too am not so sure...

 

[Lucast85]

some stay at about 4.2V. Others show 3.7V.

This is why lithium cells needs of battery management systems with charge balancing.
Note the State of charge (SOC)/V characteristic of lithium cells: at high or low SOC the cell voltage vary a lot.

 

[Externet]

Battery management circuitry is for batteries; not for individual cells. The charger manages the charging recipe for a single cell.
When removed from charger as the process is finished, weeks after set aside unused, some show 3.7V, some 4.2V. Never seen an in-between value.

Lithium cells have a 'nominal' voltage of 3.7V. Where does that figure come from ? Some show 4.2V. Data sheets show mostly 4.2V charts at full charge.

Like a lead-acid automotive battery. Charging voltage is 14V. But the battery shows 12.6 at rest or 'nominal' 12. Lithiums have a charging voltage of 4.2V. But not all come down to 3.7V at rest. 8-O