I have a charging point I am going to put on my bike. What I know about electrics is dangerous so after a little advice before i mess it up.

I was going to wire it direct to the battery with a 12v fuse on the live wire but my research has revealed that the voltage fluctuates whilst riding due to variations on speed etc and I dont want to fry my mobile phone. I am also going to get a simple on/off switch so that the battery is not drained when the bike is not in use.

What I really want is to wire it to the ignition so that it will only be live when the bike is on and the switch is on. How do I do this? Ideas or offers would be greatly appreciated.