pegwatcher:
The way it's usually done (on my commercial chargers) is put a constant current into the battery while monitoring the voltage across the battery. When that voltage reaches 4.2 volts, they change from a constant current to a constant voltage of 4.2 volts and then monitor the current until it reaches a very low level (on my charger that is below 10% of the constant current level that was used in the first step)
Thank you that makes perfect sense, do you perhaps know what voltage the battery gets during constant current charge? Can this voltage be above 4.2v?