I have a 18650 battery (model protected KeepPower 3500mAh) that started to malfunction after it fell on the floor.
Here is the weird behavior after the shock:
-first, the battery stopped working after the impact.
-the battery cut-off when I test it on Turbo mode (different flashlights have been tested)
-Voltmeter shows a good 4.2V after charging.
Is these possible to repair the protection circuit or should I simply get it off and keep the battery as an unprotected cell?
If you'd like, protection circuit kits are available for little money. You'll somehow have to spot weld or solder the connections on the cell, and then put a new protective wrap over all of it.
With regular protection circuits it's pretty normal for them to cut-off when the drain strain is high (turbo modes and high drain torches as a rule). There's no other practical way around this other than removing protection circuits. Using high drain cells is advisable for high drain torches, current “3500mAh” 18650s (cough) are hardly high drain.
FireFlyMod, it is quite likely the battery protection circuit is based on a DW01 protection chip with two 8205A dual MOSFETs, and one of them ceased working after the fall.
If you really want to fix it, you can grab one of these:
In my opinion, if you're careful as to prevent leaving the switched on flashlight abandoned, there's no real danger of over-discharging a cell for most 1S torches, namely because below 3V to 2.8V they turn out noticeably dimmer and the ratio at which they're discharging the cell is already much lower at or under these voltages.
