Charging Lithium ion batteries at slow rates

When the charge rate during the constant current phase is low, the charger process will spend less time during the constant voltage tail. If you charge below about 0.18 C, the cell is virtually full when the 4.2 volts is reached. This can be used as an alternative charge algorithm. Just charge below 0.18C constant current and terminate the charge when the voltage reaches 4.2 volts per cell.

Safety

Every lithium ion battery pack should have a method of keeping the cell balanced and preventing them from being over-discharged. This is usually done with a safety board which monitors the charge and discharge of the pack, and prevents dangerous things from happening. The specifications of these safety boards are dictated by the cell manufacture, and may include the following:
Reverse polarity protection
Charge temperature--must not be charged when temperature is lower than 0° C or above 45° C.
Charge current must not be too high, typically below 0.7 C.
Discharge current protection to prevent damage due to short circuits.
Charge voltage--a permanent fuse opens if too much voltage is applied to the battery terminals
Overcharge protection--stops charge when voltage per cell rises above 4.30 volts.
Overdischarge protection--stops discharge when battery voltage falls below 2.3 volts per cell (varies with manufacturer).
A fuse opens if the battery is ever exposed to temperatures above 100° C.

4.2V 0.8A li-ion battery charger