Thoughts on 18650 protection circuit quality

You can find cheap protected cells on sites like aliexpress/banggood using Panasonic cells for example. But what do we know about the protection circuit? Could it be that some of these cells are cheap because the circuit is junk? Has anyone seen good data on these protection circuits tested or examined for quality? I know people have opinions or their own experience but I wonder if solid data exists.

I have some Keeppower cells which use Japanese IC but who knows if that's any good either. Anyway it's an important component because let's say it were junk quality plus you charge it with a $2 charger from banggood, that could equal kaboom.

I bought two protected Panasonic 18650B from China a few years ago. In one cell, the protective circuit has given up its spirit within a narrow year, although the maximum current consumption was hardly more than 2.5A. The other cell I keep on reserve. I don`t really use it, because I never trust it. - Maybe I'll make a couple of discharge tests with currents of 3 to 4A in the next time.

sbj - interesting.

I thought there would be more replies on this. I guess it's as I suspected: nobody actually has any idea and will buy any cheap junk off the discount sites to save $5 and risk burning their house down.

We no longer own any protected 18650's.

These days I'm most comfortable using unprotected Samsung 30Q's [INR hybrid chemistry] in all of our lights.

sbj said:

I bought two protected Panasonic 18650B from China a few years ago. In one cell, the protective circuit has given up its spirit within a narrow year, although the maximum current consumption was hardly more than 2.5A. The other cell I keep on reserve. I don`t really use it, because I never trust it. - Maybe I'll make a couple of discharge tests with currents of 3 to 4A in the next time.

Click to expand...

Have my discharge tests of the second battery just finished.
In order to see the current limit of a possible failure of the PCB during the discharges, I started with 2A discharge current and increased by 0.5A at each pass, with a maximum of 6A at the end.

Result: No abnormalities. The battery behaves in the same way as expected. My fear, that the protection will fail prematurely, has not happened.
The failure of the first battery protection therefore, did not appear to have been a systematic error, but was purely accidental.
Of course, this does not say anything about the failure rate.

Unfortunately, I have not found the bill. But the cells I would probably have bought in 2012. Even though they have hardly been used since then, I am pleasantly surprised, that their internal resistance has hardly changed since then. I have them stored in an unheated room at around 3,9V (occasionally recharged).