18650 battery categories / boxes / bins

[byteharmony]

Looking for people with experience building 18650 larger scale projects to answer the question:
How do you sort your cells after you test them?

I've tested about 200 batteries now. I read about testing for capacity, internal resistance, voltage drop over a period of 1 month.

What do the people who love doing this prefer to do?

@OffGridInTheCity
@Stefanseiner

Are the most notable I've seen on the form.

 

[OffGridInTheCity]

I';ve processed over 12,000 cells to date....

In my test process, I charge, discharge, and then charge using OPUSs. This leaves the cells at ~4.17v. I then let them sit for at least 2 months and discard any that drop below 4.10v - e.g. self dischargers. Some have sat as long as 6 months as it takes a while to build these packs and still were above 4.10v - a lot at 4.13v etc.

For long term (multi-year) I discharge them to 3.5-3.8v range and the seem OK after 2 - 3 years.

This is all in my home, so year round ambient temps are 70-80F.

 

[byteharmony]

You are the 18650 man!!

From our source thread post:

Solar bank with 18650?

Is it reasonable to make a solar battery bank using 18650 cells in series/parallel?

diysolarforum.com

@OffGridInTheCity:

IR wise, you need a good tester and discard any that don't meet you're standards.

Capacity wise, the charge / discharge gives you a capacity reading. I group mine in 100mah buckets. Let's say you have 100 cells from a similar source with 2600mah as the 'new specification'. You might get 10 @ 2600mah, 30 @ 2500mah, 40 @ 2400mah, 10 @ 2300mah and 10 @ 2200mah - so they're grouped into 5 buckets. Then you might say - I only want cells that are 90% of original capacity. So you discard the 10 @ 2200mah bucket as that's below you're criteria.

Self-discharge wise - discussed above.

Then you wind up with buckets of cells grouped by 100mah capacities that have acceptable IR and are not self-dischargers. At this point simply round robin thru the buckets to evenly distribute the cells to the packs until you reach the desired total ah per pack.

On a 100ah pack, +/- 2ah is not a big deal - the battery will work/balance OK. For example, in the example above you only have 10 @ 2300mah but you're building a 14s battery. So only 10 of the packs can get a 2300mah and the remaining 4 will have to get a 2400mah instead. This puts it 'off' by 200mah. Not a big deal.

I have an XTar vc8 plus. It's a bit funky, it can only capacity test 4 cells at a time so i use the other side to charge and get IR numbers.

I don't have any experience to know what an acceptable internal resistance is. A quick google search gave me:
50 - 100 - Great
100 - 300 - old
300 - 400 - near end of life
> 400 - junk.

What do you think?

I've done 2x 18650 purchases so far. One from batteryhookup, one from batteryclearinghouse.

I'm through about 100 of my 300 cells and I'm about a month into the project just using the one charger. Given your advice I'll probably batch cells every 2 months to give time for voltage sag. I've learned a lot about how to tear stuff apart doing this ? .

Thx again.