More then likely its the ECU since of course it is never a good idea to do this for one .....mainly they just take off the negative battery cable only to check how the alternator is doing never change the battery while the car is running its a very stupid idea and like mentioned above you better hope its not the ecu but im almost certain it is plus a couple fuses

 

well i dont think al try changing the battery on a car whiles still runnin again? the thing is it is only when i turn the car over that it blows the fuse for the ecu and the back up fuse as well? spoke to a mech he said it might just be a differernt amped battery i tried touse for the car which has caused a shortage in the ignition or round about that area,gonna buy a ecu during the week can get one for £25 so fingers crossed its just that and a couple of fuses? cheers for the info lads al let you no how i get on

 

They don't recommendpulling the battery on running cars without ecus.