Cell Weight as a measure of quality

[cloudy]

I've recently bought a box of 160 new QB18650 12A cells and will only use 144 for my build. So I'm trying to quickly weed out the worst ones. I don't have an accurate way to test quickly so am wondering if there are any other properties that could identify the weaker cells.

90% of them are above 46.0g, but some weigh less (such as 45.89g), would these cells be weaker given they have less of something? Otherwise, I could measure voltage to detect self discharge? All measure close to 3.50V as shipped.

 

[rafalg]

i don't think the bad ones weigh less or more (except of some junk knockoff brands with 'fire' in the name, which all weigh significantly less and have 1/3 of declared enormous capacity). But if you bought them new and they're all same voltage after many weeks since last charging then they shoudl be fine.

 

[Hillhater]

DCIR testing would be a decent first test,..short of a full capacity test.

 

[docw009]

Looks like non brand name chinese made batteries from aliexpress?

You can get an ACIR meter like this one, Many 18650 cells are specified for AC IR these days, The measurement take a few seconds. Since these cells are new, all of them should have the same IR. Any outliers would be suspicious. If you're going to make battery building a hobby, it's a useful tool, and a small cost relative to whatever you paid for those 160 cells. The meter also works as a pretty good voltmeter too.

 

[neptronix]

You'll have to cycle test them, sorry!

A good RC charger could help.. you could cycle test 6-10 of them at once.. just need to build some battery holders.
Worth doing!

 

[cloudy]

Thanks for the responses, yes the cells are Chinese made cells. Thunderheart has done a review of them here and from that I decided they would be ok for my purposes:
Queen Battery QB18650 2500mAh capacity test + comparison with QB18650 2600mAh
Sounds like weight is no indicator of cell quality, I'll put the scales away!
What would be a good RC charger than can test 6s or 10s? I'll look into IR measurement also. Postage is rather slow to where I live so probably adds another month delay onto the build.

 

[Hillhater]

Where in Oz are you ?
There used to be a local Hobby King distribution center in NSW (Moruya) , but i think Covid killed it !
Search for a good local hobby shop that specialises in RC kit or Drones… they all need good chargers.
My go to online is still HobbyKing for things like chargers etc.

 

[amberwolf]

90% of them are above 46.0g, but some weigh less (such as 45.89g), would these cells be weaker given they have less of something?

Do they all come with insulator rings under the shrink at the positive end? If some are missing, they would weigh less.

 

[cloudy]

Yes, all cells have the white insulation rings.

 

[jonyjoe303]

for new cells I would just use an IR tester, that will weed out the weak ones. Some cells pass the capacity check, self discharge and still have high IR. Cells with high IR will cause balancing issues later on. I myself wouldn't waste my time building a battery pack without testing the IR. Even with new cells it would be a good idea to test for IR, all it takes is one bad cell to give you problems.
Before I got an IR tester, I had many problems with packs not staying in balance. This is the IR tester I use, best 50 dollars I ever spent.