A good friend of mine called one day and asked me if I could build him a Li-Po Charger. His Girlfriend wanted to go hiking for some time and needed a way to accumulate solar power for her electronic gadgets.
So I designed and build the circuit in just a few days, though I needed about 3 weeks for it as my free time was a little low.
Measuring of voltage and current is done with the help of TL431 Precision References, wired as PID-regulators, and tied to a Switched Buck Regulator for high efficency. I also implemented an electronic switch for shut-off with integrated discharge and under-voltage protection.
The whole assembly found its way into a plastic cycling-bottle, so it can easily be mounted on a bike: