TESTING 18650 BATTERIES

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gsc1ugs

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I have a lot of 18650 batteries out of makita batteries i need testing because the makita charger doesnt like them, need to test if the cells are dead because most will charge up individually using a cheaper device and read around 4 volts each but when together the makita charger said its bad. I do know if one goes down the whole 18v battery wont work
 
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The best device I know of is an Opus BT-C3100

They can charge, discharge or test up to four cells at a time. I use mine regularly for testing salvaged 18650 cells.
 
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I would suggest the Xtar VC8 charger - it has 8 slots and will charger 8 18650's (or others), PLUS it will cycle, test, and measure ones in slots 1-4. It gives you a nice capacity reading.
 
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gsc1ugs said:
Do either tell you if battery is useless?
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The Xtar VC8 one I have tells you the cells measured capacity (grad setting), so you can easily tell if it's good or not - it will also tell you if a battery is completely useless. I've just used it the last few days to test cells from some failed battery packs - all but three checked slightly above their rated capacity, the three faulty ones all failed the initial part of the testing.
 
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You can sort out all batteries by a heavy load test identical for each battery then sort and match all by voltage. For say a 5 Wh 3.6V cell , use some 10W resistor that draws 1-2 A for each minute measure exact voltage and match within 2%. Otherwise the weakest will die rapidly again.
 
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Looks good but if one does not have a balancer in the design, the battery capacity of grouped cells must be matched

- If mismatched battery capacity cells are in a string then the weakest cell will discharge faster and under/over charge faster - if it drops well below 0 to 10% SoC voltages or over Vbat max , the battery will oxidize (insulate) rapidly with very high ESR.

Furthermore, if a pack has more than 1 bad cell, changes are high all are end-of-life, but may have some application with < 10% as an ultracap.
 
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I'm not quite sure what those comments have to do with the charger? - as each battery is charged separately, there's no balancing involved.

And as for balancers, I've recently started removing them from one of our products, as we're having a few battery failures - caused by the balancers themselves failing. So we'll see what happens without them.

In fact, I've been using the charger to test the calls from the failed packs - I built new packs with brand new cells, but tested the old ones for my own use
 
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Balancers are only used in strings not single cell chargers.

Balancers must be designed to dissipate the power dissipated during CC mode at the the C rate used in the system for which the batteries are rated, in order to bypass when one is fully charged. The last charge capacity during CC mode is what 10% so balancers are often expecting batteries to be balanced within 1% and when a cell degrades to 10% they burnout. The balancer design ought to indicate this state before they fail.
 
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Tony Stewart said:
Balancers are only used in strings not single cell chargers.
Click to expand...

I know, which is why I was puzzled by your previous post?.

Commercial balancers don't usually indicate anything, as they have no displays.
 
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"if one does not have a balancer in the design,"
I was not referring to your charger rather the product design such as a car or Bank system

Most consumer product chargers I have use the LED to indicate:
- too cold, if a temp sensor is included,
- too high ESR (flashing LED)
- charging and
- fully charged, all with LEDs or bicolor LED.

- but these packs that I use do not have an internal BMS

For a decade or so there exists smart BMS that use FET and coil with regulator chip for each cell to share excess power rather than drain power into heat to equalize cell voltage.

e.g. https://www.flashbattery.tech/en/bms-functioning-and-vehicle-integration/
 
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I am salvaging 18650 batteries too. My charger will not charge a 18650 if voltage is less than 3v. Anything 3v and up I can charge. Batteries less than 3v I put in parallel with a 4v battery to charge it above 3v. Once battery is above 3v the charger will charge it. I charge 40 batteries then return a month later to test them. Batteries 4v I keep. Batteries less than 3v I trash. If batteries is a bit low like 3.7v I charge it 1 more time to see what happens after 1 month. If battery is low again I trash it.
 
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