I just got an Xtar VC2 Plus charger and two of their 2600mAh 18650 batteries. When I first put them in to charge, it showed over 3 hours to go, and that time gradually went down to around 2:30. Then I looked at it and one of them was up over 4 minutes. I switched the batteries around, just for the heck of it, and both times were around 2:30 again. I looked again just now and one is up to 4:30, and the other is up to 3:42.
I have no experience with chargers like this or with 18650s. What’s going on?
I don’t have the Xtar VC2 Plus, but based on the above description review, the estimated time left is only a very rough estimate.
Based on my limited experience with charging various 18650s, the initial charging time usually can be esimated if we know the capacity of the battery and basing on the charging current. (I don’t think the charger will know ahead of time if what’s the capacity of the battery it is charging, but is doing continuous estimates based on how fast the voltage rises…)
However, the ending current (CC/CV or constant-voltage - constant-current phase), the ending current will gradually taper off, and higher-resistance batteries take a much longer time to taper off.
(I notice the Samsung 30Q and Sony VTC6 have a pretty fast tapering-off time, as both these are low-resistance; but on older batteries, the ending charging time takes a very long time to finish charging).
So if the battery is a high-resistance one, I would presume that the charging time (near the end portion of charging) will take a very long time and it’s hard to accurately estimate how much time left before the battery becomes really “full” 4.20v.