Is it normal for li-ion cells to drop voltage in just a couple of days? I have new cells and I’ve noticed that hot off the charger, they read 4.18 then after 4 days they all are at 4.13. The batteries are Keeppower 3400mah 18650s and the charger I’m using is the Xtar WP2 II. I’m using a cheapie DMM and don’t know the accuracy but since all the batteries read the same, I doubt it’s the DMM.
Btw, can anyone with a calibrated DMM confirm the voltage of a battery hot off the Xtar WP2 so I atleast gauge how accurate my DMM is please.
The DMM may not be accurate but the difference you see should be close. My Panasonics usually drop .03v to .04v a day after charged. The important thing is what is the voltage after a couple days or a week. If it’s still hovering around the one day number their fine. If their still dropping in voltage it maybe time to toss. You are seeing a .05v loss after 4 days I would say that’s acceptable. If the DMM is off by .03v then your batteries should be around 4.16v after four days given what voltage numbers jackey gave.
It’s normal, that the voltage drop between “out of the charger” and “one hour later” or more.
Don’t measure directly out of the charger. Wait an hour and then measure. I think this will be a realistic result and the voltage will not drop more in the next days.
Its possible that the charger terminated early. Its more important that they hold their voltage in days. Usually a bad cell continues to drop voltage over time rather quickly.
how quick is quickly? I topped them off last night to 4.17-4.18 volts right off the charger and so far after 10 hours they still show 4.17 volts.
Also, I was thinking of getting a fluke DMM but they are expensive. I’m wondering if the lower end models (ie. 116) would suffice for our uses or should I get the 179 or 87-V?
If it drops to around 4.00v within days of charging its toss it time. If it drops to 4.10v within days of charging its on its way to being tossed out generally. New cells will generally hold there voltage (measured one hour off the charger) for days dropping maybe .01v to.04v. The amount of voltage drop after days off the charger is a good indicator of the cells health, a capacity test could also give you indication of a cells health.
I have a 87v but its not necessary for measuring cell voltage. The flukes are good meters and last forever but most any cheap meter will work for li-ion testing even the $5 HF meter works well. If you want a little better meter this one also good. Its a rebrand Mastech MS8229. It measure close to the same as the 87v. A thread that might interest you.
I date all my charge times by writing them on my pack pulls to get an idea of the cell’s health. I just had some Samsung pink 2600s and some Panasonic 2400s stay at 4.20 for a solid two months. Not 4.17 or 4.19, but 4.20. I’ve also had cells go from 4.2 to 2.5 over night. :–0
BUT with new cells, I’d cycle ’em at least 10 times (maybe more), down to 3.7 or so and then recharge with maybe 12 hours between cycles before making up your mind. That seems to work the best for me and I’m keeping alive about 200 18650s and 14500s right now (motsly pack pulls). I toss anything that drops from 4.2 to 4.15 over 2 weeks to a month. I find that drop means the battery capacity ain’t great. Of course there are exceptions.
But try cycling them. I have had quite a few pack pulls — and even a few dicey new batteries — come back from unusable charge-loss levels with cycling to become top performers. In fact, it continues to amaze me how many pack pulls keep their charge better than “supposedly” new batteries. I don’t know if this is because the batteries get more stable with cycling or if the newer cells aren’t as good as the older ones. Or maybe the pack pulls are real and the new batteries are not? I don’t pretend to know why, but I have observed it many times now.