Please can anyone advise, I have a Spark and ive been told that I can charge it via usb cable and plug, I've never had to do this as I have the dock for 3 batteries, but I thought I'd try it, when I plug in the usb lead via a plug the lights on the battery don't shine green, but I do notice a light dining at the front of my spark and after a while the spark gets warm? Can anyone help! The usb does work if I plug it into a pc to transfer any images or video.

Are you using the DJI usb power adapter?  If not, you'll need a power adapter that puts out at least  2 amps.  The Apple cube that comes with a recent iPad would work but not the one for the iPhone for example.