numberonebikeslover said:
Having 60% of my cells at 4.09 state it was quite disappointing for knowing the fact that they are not worth.
Take one of those cells and connect a load to drain it at C/2 rate, then monitor the voltage, current and time it takes to reach the bottom--there may be quite a bit of useful life in there and you won't know unless you test them. You would do yourself a favor to test each cell, and you would do even better (having no BMS) to bottom balance all your cells after determining the actual capacity of the cells. If you bottom balance and then only charge up to the level that fills the "weakest" or lowest-capacity cell then you can safely operate without a BMS and may be able to get some useful mileage out of those cells.
Don't keep trying to charge them to hold the last little bit, overcharging is how they get permanently damaged and can explode. Old used cells are "worn out" meaning they have lower capacity than when they were new, and they will never hold nor attain the original capacity, but there may still be useful life left for your application.
You may already know all this, but how do you determine capacity? Depending upon the chemistry you will have spec voltages for charging and discharging. Set up a load to drain each cell at 1C or C/2, C/3, whatever you feel comfortable, and monitor and record the voltage, current and time it takes to reach the specified lower cutoff voltage. Current x time gives you capacity in amp-hours. Then CC charge the cell at C/3 or whatever rate at the CV cutoff voltage and monitor/record the same. You don't want the cells to ever get hot or puffy. A puffed out cell is definitely bad and not worth using.
Then drain them all again with monitoring/recording to determine capacity number again, then put them through a bottom balance procedure to prepare for charging as a pack. Each cell will have a different capacity and you can determine the "weakest" one, and only charge your pack until that one is about 95% full and not have to worry about fire or explosion in the situation of no BMS. The top and bottom 5% are fairly useless due to having the highest voltage sag and it's not worth the extra time trying to squeeze a few more in versus the fire risk of overcharging.
Good luck to you, i admire your ambition, spirit and will-power to make it happen!