Re: Where should I start
"It will charge my galaxy s but if I'm using satnav, the screen and GPS use more power than the charger can supply."
That means the charger doesn't have the d+ and d- pins of the USB shorted. Modern phones will only draw minimal power from a USB port unless they know it's a charger. My HTC is the same, I have a similar looking charger for my car capable of supplying 1A. I had to make up a special charging only lead that shorts the pins out. Without this the phone barely charged, and using satnav would cause the phone to slowly discharge. With the new cable charging is the same as from the mains.