Barkuti, sorry for the long delay but I’m back with numbers and a happy report! Wow, this new forum platform will take a little getting used to. I rather like the old layout - less busy, easier to function, lots of little details - but I can see areas with a lot of great improvement here on the new one.
Ok, so last we talked I’d planned on starting on that upcoming weekend. I ended up charging them up the next night I think, but made an oops and just let the charger top them off as usual. So that provides another data point for a few days’ worth after full charge. I drained them and charged them up to the right spot, then took daily readings over the next - well now it’s been a week and a half.
I kept the notes in a draft email, and as a test I’m just going to copy/paste from there and see how it formats. Bottom line is that these two cells have stayed stable the whole time after the expected initial slight drop with rest after the charge. I’m going to keep this going for a few more weeks just to see what they do. These are the only two of this cell that I own and I think they only have maybe 9 or 10 cycles on them (not a popular cell for my own uses). I have some of the higher capacity Vapcell F14 cells as well and will probably do this test on them soon (they seem to be stable, but as with these Keeppower that’s mostly anecdotal until actually observed/measured over time).
Ambient room temps were 20°C most days, but from 19°-22°…don’t think that matters here really.
Initial accidental full charge was started from the cells drained-in-a-light down to 2.783v and 2.831v followed by a 30min rest period.
Miboxer C4-12 (single button version) charged to 4.2v at 300mA. Cell ends and charger contacts were scrubbed and cleaned with IPA before charging.
Input at termination (for what it’s worth) showed 1048mAh/1030mAh
IR is totally not accurate or trustworthy on this charger, but it settled on 110mOhm as charging progressed (was 183 and 200 mOhm at start)
Immediate voltage reading after pulling off charger was 4.157v / 4.156v
One hour voltage 4.155v / 4.155v
After four days 4.149v / 4.150v
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Now for the real test.
Noting the slight undercharge at termination on this charger, I tried to gauge when the right time to pull them would be so they would end up at the 3.9v you requested. I actually hit it spot on - not sure how that happened!
Drained-in-a-light down to 2.979v / 2.944v with a one hour rest period.
Charged at 300mA to 3.94v (I tried to give them the exact same charge time/time delay before pulling them after reaching that voltage - because science).
Input 774mAh for both
IR settled 98mOhm for both cells (used slots 2, 3 this time because slot 1 always seems erratic…initial on both was 220mOhm)
Temp reached 24°C (21°C ambient)
Immediate voltage reading of 3.900v and 3.902v
Voltage after one hour rest was 3.895v / 3.894v
Over the days we lost just a few millivolts, mostly on that first 24 hour period. Something interesting was that when I would read on Cell #1 the voltage would usually climb just like a single millivolt or not at all, after the usual few seconds’ wait. Cell #2 always seemed to climb up 3 millivolts, every time except the last couple where it was one or two. I don’t know if that says anything about the cell (would be curious if it does) but it’s not the meter. Daily results as follows:
Day 1 3.891v and 3.890v
Day 2 3.890v and 3.890v
Day 3 3.890v and 3.889v
Day 4 3.890v and 3.889v
Day 5 3.890v and 3.889v
Day 6 3.890v and 3.889v
Day 7 3.890v and 3.889v
Day 8 3.890v and 3.889v
Day 9 3.890v and 3.889v
Day 10 3.889v and 3.889v
I really expected to see just a bit more drop - initially and over the days - but I’m glad to see that these are this-much stable and happy. I’ll keep noting the readings and post back here in a few weeks.
I don’t expect much from these tiny cells that also aren’t made by the major manufacturers, but hopefully these will give a pretty good cycle life and capacity retention. Who knows if they’ll still be available for sale in a few years’ time, but it’s good to share the data points.
I wonder what Limsup’s cells are suffering from…maybe poor storage before he got them, or perhaps Keeppower isn’t very stringent about cell selection? I suppose that isn’t the worst drop over nearly three months for these tiny cells, but I wouldn’t be very happy with that either. China-brand or major OEM, I’ve never had cells drop that much in storage until they were already very well used and not liking a full 4.2v charge anymore and some capacity loss was clearly apparent.
Now…a question for you. Why did you specify 3.9v for the test? Obviously there’s more loss initially from the full Overcharge we tend to give these. Just curious.