Lion cell charging

[Matthew98]

Hi. Is it ok for a lion cell to raise up to 4.23 V ? This is the reading of my V meter (quite cheap) while charging with repaired Imax charger. It does its thing raising the voltage from 4.2 to 4.23 V and again and again for the cell to hold the charge better, but is it ok in this range ? I thought it was suppose to be 4.18 to 4.2 or something... Thanks !

[MrAl]

Hello there,

In a perfect world the voltage can go up to 4.250v but we dont live there we live here.

What this means is that since we dont have a perfect volt meter, we have to be a little careful, and that means we should go under 4.200v just slightly.
For example, if your meter reads just 1 percent low, then 4.242 willl read as 4.200 and 4.290 will read as 4.247 so it will look high but possibly ok when it is really over the limit of 4.250 and over the recommended 4.200v.

A secondary issue that comes up is that longevity of the cell.  The higher in voltage, the lower the life span.
I keep mine charging up to 4.150v and i use a special highly accurate voltage reference to make sure my meter is reading properly.  The benefit is longer cell life and the drawback is a little less charge held in the cell.

It is important to use a good meter for this kind of measurement.  For example if the meter is 5 percent low it might read 4.200v when it is really 4.410v which is much too high.

[Matthew98]

The meter showed 4.25 at the end of the charging cycle, but when the charging cycle was done, it was spot on 4.2V. I use this charger for charging it fully and than measuring its capacity by discharging, so the cells are charged by this charger only few times ... What im worried about is going it all "bang" ))
I might buy a voltage source for checking the meter accuracy, though. I saw few precise ones on ebay and I belive Julian Ilett reviewed them.