Begginers Guide to Processing 18650 Cells | Cell Database

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Another UK member
You check their voltage first and separate them into two groups, low voltage and normal voltage. Low voltage is everything from 0V to ~2.5V, everything above is considered normal. I don't know if or where the Opus makes the cut between chargable and not chargeable cells. Most charger reject a low voltage cell if it is under a certain voltage.

Low voltage:
Charge with a small current. The lower the voltage the lower the current. If at 1V or below then 10mA is plenty. Don't know if the Opus can do that, you can use any CC/CV power supply for that. With the voltage going up you can also adjust the current to make the process faster. At 1.5V you can go up to maybe 50mA, closer to 2V you can go for 100mA. There are no definitive rules for this, it is a matter of the right feeling and most people, me included, are probably overly cautious.
You let the cell charge until 3V or so, above 2V you can raise the current to 200 or 300mA to make it faster. After that the cell goes over to the other group.

Normal voltage:
Charge the cell at 1A. Check its temperature, it shouldn't get warm. Once charged, discharge it at 1A. Check temperature again, it shouldn't get warm. Or hot, better say hot. If you don't have a infrared thermometer you can just touch the cells. If they feel warm they are above your bodies temperature. That's ok. If they feel hot they are way above your bodies temperature and that is too much -> bad cell.
When the discharge is fnished and the cell didn't get hot you can write down its capacity. If it is really low you will probably chuck them away. You have to find find your own thresholds there. I binned every cell under 1000~1100mAh. I kept every cell between 1100 and 1500 for smaller projects and testing. And at 1500 or above I sorted them into groups like 1500-1700, 1701-1900, 1901-2100, above 2100. What is suitable for you depends on the results you get und what you want to achieve.
You then charge the cell again and let it rest for some time. Check the voltage after a couple of days or weeks to see if the cell kept its voltage. Everything above 4.1V is fine, everything above 4.0V is ok. Below 4.0V isn't really.

Repeat until out of cells Smile
zag2me likes this post

With opus run discharge test mode. If to low voltage bump charge them over like 1.5V as DarkRaven said.
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