Yeah, I would not trust the readout on the Anduril firmware. Consider the voltage check on the sofirn (or any Anduril light) as just a close-enough guideline to help you know how much time you have left (or, say, if you’re a guy that only wants to run his cells down to 3.5 volts before charging, then it helps for that scenario).
The SC31 Pro comes with original Anduril and the voltage check cannot be calibrated. In Anduril 2 they added that calibration feature and you can change it in .05 increments…but of course for that you would want the truth-telling accuracy of a multimeter so you know what the voltage of the cell actually is before telling the light what it should say. This isn’t critical, though…that’s not the light’s job really.
The charger shouldn’t have overcharged it to the point of rising voltage. When the battery is full, the charger will not completely shut off but the charging current drops WAY low so it’s like a very slight trickle charge. Not enough to increase voltage or capacity any meaningful amount.
Ok, so don’t let this feel too techy, but here’s a testing measurement graph from HKJ’s review of this charger that might help you understand what’s happening. It’s showing several things but what we want to look at is the red line and the red scale on the left margin…this is voltage as the cell started on the charger (left) and then completed its charging (right). But bottom line is that the charger is likely accurately-correct while the feedback from the firmware in the flashlight is not…but without a multimeter you just need to have some faith.
Looking at the red voltage line, you can see that when he first puts the battery in, it’s reading just under 3.5 volts. And it charges and charges and the voltage rises gradually and it keeps on charging and then somewhere around 2-1/2 hours it reaches the point of about 4.15 volts. And then the red voltage line starts to get flat instead of continually rising. This marks the almost-end of the charging process. After all that running it’s time for a cooldown lap. What happens now is that the charging current starts to diminish rapidly…a good charger like this one will taper down so that the voltage does reach that nice 4.2 volt top off (or really close) but the current is low and gets lower and lower. This gives the cell time to cool off a little and take that last final bit of energy for a good complete charge.
This brings us to the darker green line (ignore the bright neon green) and the green scale on the right margin. This is the charging current that is going in to the cell throughout the charging process. It starts way up top, pretty much on the 1,000mA line…which is 1 amp. He selected the 1 amp charging rate for this test. The current stays constant, like filling up a pool with a hose. Now, right around that same 2-1/2 hour mark you see the green line cross the red voltage line….and then poof….the bottom falls out and the green line plummets to the bottom quickly. That’s the charger saying, hey, we’re about done here, taper off so we can go home boys. Takes a little time for the current to drop all the way down to that minimal trickle charge level (HKJ stated that it was 70mA). But at this point there’s basically almost nothing going in to the cell.
That said, since it doesn’t totally shut off (many chargers don’t) it’s wise to remove the cells from the charger not too long after they have finished their charge cycle. You won’t hurt anything or risk overcharging them if you forget and leave them on overnight or something, but it’s just best practice to stay attentive and pull them out when finished. There are some poorly designed chargers that might actually hurt the battery or worse if they exhibit bad termination characteristics, but this is not one of them. It’s doing a great job.
I guess this is like filling that pool with a hose but then right as it’s almost full you reduce the amount of water so that you can juussst fill the pool without making it overflow. I think onboard charging circuits inside of flashlights mostly do the same thing, less sophisticated, and it seems that they vary a bit as far as when they decide that they’re “full”…but not in a disadvantageous way or a dangerous one…just not as accurate as a good dedicated charger.
(I can’t seem to get the direct link to the pic to show in this post….so a link and then just a link to the review and you can look at the first graph that you come to)
http://lygte-info.dk/review/Review%20Charger%20Xtar%20VC4%20UK.html