Vikas Sontakke said:
As far as I can see, the Nano RCR123 charger seems to be very gentle and does not overcharge the cell even if the cell is left on it for overnight. It cuts off at 4.18 or somewhere around that range. I have heard that Ultrafire charger can lead to overcharged cells but I don't have personal experience with it.
- Vikas
and another FYI, lithium chargers fill the cells about 80% within the first hour of charge. it takes another hour or so to get that last 20% in.
there is some variation in how high the final voltage gets on a resting lithium. 4.22, 4.25, 4.17... etc. Some of the crazies turn a pot to increase their chargers final voltage readings, but it seems like a very risky move for a tiny amount of power.
all lithium chargers (when working correctly) will taper the charge to about .05A for last few %, and will never "overcharge" a cell, even if you leave it on overnight.
(of course, you're home, and the cells are away from anything flammable, right!?)
lithium cells are an incredible mix of great low-temp performance, low self-discharge, high energy.
however, they take a couple hours to charge, and can be damaged by discharging too deeply, and fail in a way that most people would consider dangerous.
be safe, go and read some sites on unprotected lith-ion safety.