How to charge a 3cell 11.1V battery pack made out of 3 Nokia BL-5C?
You cant simply use your cells when they are in series across the terminals of the outer cells. If one of your cells has(and they are all different) a significantly lower capacity it's voltage could drop below 2,5V and damage the cell before the voltage overall gets too low to shut down. You'll have to use a Lithium Balancer for this to work. It tries to keep the cells at the same voltage while protecting them.







simulate this circuit &ndash; Schematic created using CircuitLab

This will evenly charge your cells. I also recommend a protection against over-discharge, overcurrent and backfeed.
The Balancer/Charger and Protection can also be combined as one unit.

A board like this has several protections build in:
4A 3S Lithium Battery Protection Chip Board