Are the Lipo’s that have failed the same brand? CycloneFPV found they had some bad Auline Lipo’s shipped to them the other month. Ian (Madtech) also had two relatively new GNB packs go into self destruct mode on the charger, within days of each other. It’s also worth noting that many brands come from the same production line but have a different suppliers label on them.
Is it the same cell that is dying in the pack? If so have you checked the continuity of the balance lead with a multimeter. Even though a charger or cell checker (did you use a separate cell checker?) will not read a cell’s voltage if below a certain value a multimeter will. Very rarely does a cell go to zero Volt, it will still have a residual voltage even if just a few hundred milliVolt. If you check the balance plug with a voltmeter you will be able to tell if the cell is really bad or that you have a broken connection to the offending cell.
In the picture below I’m showing the wiring 2S and 4S balance plug.
If for example cell3 of the 4S in the picture was suspected as being bad, to measure the voltage you would take a reading on wires 2 and 3, counting from the right. If it’s reading zero Volt then it can be assumed that there is a broken connection on the balance lead. If the cell is reading a similar voltage to that of the other cells in the pack then the fault will lie with the chargers balance output.
If these cells/batteries are going bad prematurely, and are recent purchases, I would certainly be having a word with the supplier you got them from. Any reputable dealer would be appreciative as the last thing they want is to be sending out potentially dangerous products.
I will hold my hands up high and admit I am one of the worst examples of LiPo care but out of all the batteries I own or have owned I’ve only had one lose a cell even though I’ve treated it with kid gloves. To have more than one fail in such a short period of time despite following the correct guidance, which you have, would lead me to believe that there maybe a faulty batch.