18650 RESISTANCE?

[jimmyhackers]

hello,

i recently noticed my 18s 4p lipo with pkcell 18650s in it had one cell that was about 0.2v lower than the rest after a discharge/usage.

taking the four 18650 cells out, 3 have an internal resistance of 140ish ohms and one has an internal resistance of over 200 ohms.

after leaving them not in parrallel, The one with the higher resistance has decided to raise itself to 3.86v and the other 3 have shrunk down to 3.65v.

i figure just the one has let go and the other 3 are ok. is this the case?


(on a side note, i tested an 18650 cell out of every other good cell and they are all around the 140ish ohm mark.)

 

[flippy]

Yes, if they self discharge you need to toss them and replace them

 

[Volt_Ampere]

No way resistance should be that high. Should be in the mili-ohms. How are you measuring that? You can't use a regular ohm meter on any sort of battery cell.

 

[jimmyhackers]

im using my battery resistance meter on my turnigy accucel 6. your right, my bad, it did say mOhms..

im not sure how accurate it was, but it seemed very consistant....desipite mulitple re-seatings in the same holder.

ill try and clarify... out of 4 cells wired in parrallel at 3.7ish volts.

when taken apart, 3 read 140ish mOhms and went down to 3.6ish volts
one read over 200 mOhms but went up to 3.8ish volts.

after being left for a over a day, none have self discharged anymore than after the initial change in voltage over 2-3 minutes after seperation.

which ones are more knackered.. the three or the one?

 

[jimmyhackers]

on a side note for my own sanitys sake i checked on 18650 cell from everyone of the other 5 packs of 4 that wernt playing up and they all read 140ish mOhms.

ive swapped out this one cell....so far so good. much less of a difference after a ride.

out of 72 cells its seems ive had one bad apple.

 

[flippy]

charge them all to full and leave them for a day and check self disharge

 

[jimmyhackers]

none are self dischargeing. (hence me asking)

i already know a self discharging battery is a gonner.....

these arnt, but they show vastly different resistances......

after disconnecting them in parrallel they didnt self discharge......three sunk in voltage then settled and one (with silly high resistance) rose in voltage and settled.

as i said though.....i have replaced the one with the high resistance and the battery is fine again.

this just seemed like a weird phenomenom to me hence me pointing it out n asking bout it.
i would of expected some self discharge (but it didnt see any) i also expected that the cells that dipped in voltage after being disconnected would of been the knackered ones...but they wernt.....

 

[999zip999]

Check the high voltage cell again please.

 

[flippy]

wrong topic.

 

[Hillhater]

Flippy,.. what has testing SLAs got to do with this 18650 question ?

 

[flippy]

Flippy,.. what has testing SLAs got to do with this 18650 question ?

sorry, replied in the wrong topic.

 

[jimmyhackers]

Check the high voltage cell again please.

i just have, its been sitting since my last post baout 3-4 weeks.... the voltage is at 4.06 and the resitance is still around the 200ish mark.

very weird....it appears to of charged itself......its gone from 3.85ish volts upto nearly full for a li-ion.