Calling SOFIRN: detailed data on your 5000mAh 21700 battery needed

[dmenezes]

@dmenezes

Right now I’m discharging the battery to 3.73V for storage, let’s see whether and by how much the voltage shots up at the end of it; if it’s substantial, IMO this would also corroborate that the battery needs to be discharged according to case 2 pointed above in order to reach nominal capacity.

Curiously, the battery voltage didn’t go up at all once the discharge-to-3.73V-for-storage procedure ended: it stayed exactly at 3.73V even after waiting for almost an hour. This seems to indicate that, at least for discharging down to storage voltage, D.REDUCE is actually unnecessary and should be set to OFF for this specific battery.

[Barry0892]

@dmenezes

Sure, but once reaching those 2.5V, there are two ways to proceed:

1. discharging stops at once, or
2. keep discharging but reducing current so as to keep voltage at 2.5V until said current reaches value X mA and then stop. In this case, X is what is called “reduced discharge current” and what I need to know is what its value is.

So, what I need to know is whether it’s 1 or 2, and if 2, I need to know what is the value of X.

Please, can you get back to the manufacturer and ask for this last remaining detail?

TIA!

Hi, It is the first one,
The discharge stops when it ends.

[dmenezes]

Thanks for the confirmation, @Barry0892! Really appreciated, and it’s a pleasure dealing with a responsive vendor like you.

[texas_shooter]

dmenezes, I want to thank you for the work and listing your findings. Keeps confusion at bay and enlightens.

[dmenezes]

@texas_shooter

dmenezes, I want to thank you for the work and listing your findings. Keeps confusion at bay and enlightens.

Thanks for the encouraging words, I really appreciate them.

[dmenezes]

@Barry0892

@dmenezes

Sure, but once reaching those 2.5V, there are two ways to proceed:

1. discharging stops at once, or
   (…)

Hi, It is the first one,
The discharge stops when it ends.

I found that strange because, besides my battery not reaching its nominal 5000mAh capacity when I tested it that way, that was the first time I see a Li-Ion battery where the manufacturer does not recommend a residual discharge current (aka D.REDUCE) for the battery to reach its nominal capacity, but I checked and this seems to also be the case for the Lishen LR2170SD(03BCEA5) battery that Sofirn reportedly used to wrap previusly.

Anyway, a single test like the one I did so far is not enough to reach any conclusions, so I plan to keep using (and recharging) that battery in the weeks/months that will follow and I will come back here and update.

[duckie]

I’ve seen many Li-ion datasheets and I do not recall any that specified a residual discharge current as part of the standard/rated discharge process.

eg.

[dmenezes]

@duckie

I’ve seen many Li-ion datasheets and I do not recall any that specified a residual discharge current as part of the standard/rated discharge process.

Interesting, thanks for pointing that out. Out of curiosity, what cells were these (the ones in the “eg” screenshots you included)?

[duckie]

MJ1, 50E, and a BAK 21700 cell