The car is an RS turbo converted Mk4 Cabrio and the main problem is that the car won’t drive!

The car was standing for about three months before my mate bought it, the old battery was charged up and the car fired up straight away, oil and water levels were fine. He drove the car around all Saturday afternoon as you do, but decided to go to Halfords and buy a new battery for it. He put the new battery on drove it again for a short while, when it started to splutter and run like a complete bag o shite! I did a compression test and everything was fine, changed the leads and plugs, fired it up and it idles no problem. When you try and drive it though it splutters and stalls! Anyone got any ideas? Could it be the coil because I know he moved it when he changed the battery (it had been relocated near the battery when it was converted from XR3I) Help!