sorting out defect or bad 18650 cells?

[notger]

hi

I just recently got tons of used makita BL1830 batteries.
My main idea was to put in new sony vtc4 cells.(what I do right now)

After rough measurements i found out that around 200 of the 300 cells are still holding voltage of around 3,9V
That's why i came up with the idea of building machine batteries or a spare ebike batterie out of the leftovers.

My plan would be:
1. Putting all the cells apart
2. sorting out all of them wich held voltage
3.charge them to 4,1-4,2 volt
4. let them sit for one week
5. measure them again
6. measure the voltage-drop on a 5A load
the next step would be really timewasting and i'm not sure if it's worth doing it?
7. testing the capacity by discharging it with a wattmeter

Any inputs to this plan?

And now my questions to you

- Wich kinds of defect on 18650 cells do you know?

- if i measure voltage on a bank (they are 5s2p batts) of 2cells can it be that one cell is still defect?
(most of the defect cells i measured have negative voltage)

- is it just possible to find out about the restcapacity and the function of the cell with a measured discharge, or is there something simpler

- Do you know of any application wich measures/tests liion cells in bulk

- Any other ideas, -> except that this is a bad idea

thanks

Gernot

 

[bowlofsalad]

https://www.endless-sphere.com/forums/viewtopic.php?f=14&t=26383 You might read and search for your answers in this thread.

To search in a specific thread rather than the entire forum, while viewing a thread there is a search box in the upper left, use that instead of the one in the upper right.

 

[parabellum]

From experience perspective, good cells in 1 pack are almost same capacity/resistance/performance . Take out bad pair (or two) of cells and jumper the rest, then capacity test them in bulk to conservative discharge point. I did it so with Icharger, connected to balance port with crocodile connector I made.

 

[Matt Gruber]

7. if they hold a charge they are an asset. can always add an extra cell(s) if you later discover a weak p group. i have not capacity checked most of mine from 11-13, just a few to get an idea. i find sony V to be consistent and reliable. mine are from drbass. he has an expensive tester and does not ship low capacity cells.

 

[dnmun]

doing a capacity test is not so difficult. just use a wattmeter and make a series of these little cans to give yourself enuff voltage so that you can get at least .5C or so discharging into the load you use. then just record on the can the capacity as it hits 2.7-3V. then you can remove that can from the string and continues discharging the others until you have an idea of the total capacity of the remaining cans.

i went through about 400 pouches building up my big 87Ah ping pack i made from recycled ping pouches. scrapped about 40%

 

[999zip999]

It's a lot of time and work to make a working pack out of unknow used cells. Becareful as the pos. tab can short on case which is neg. Easier to solder on tabs so don't rip everything apart.