Have I gone mad? No! It is possible to charge your cell phone using a simple fruit: the lemon.
How does this work?
The lemon juice acts as an electrolytic solution for the two metal electrodes. Usually these are something like nickel and copper. If you used higher quality metals (such as magnesium and copper) you'll get a higher PV (potential voltage) which means you won't need as many lemons. I've even seen cars powered by lemons! You just need an awful lot.
But it's important to realise -it's not about how many lemons, it's about how many electrodes you have.
Anyway, about the charger. I tried this with an old Nokia I had lying around. It requires 5 volts at 100 mA to charge, but this was a bit 'hit-and-miss'. It did charge but not consistently like when at the wall. I'm working on a booster to try and get this lemon to really work!
How to Charge Your Phone Using a Lemon
All you need to do is rig up half a lemon with the two metals I mentioned. Then slice your charger cable and connect the wires to the electrodes. Then just plug in your phone!
Here's a video of some other cool ways to power stuff!