Lumpy2812

Hi, I know this has been asked so many times before and I promise I have read through a lot of previous posts but can’t fix the issue. Engine lost power and is running rough as guts with ESC and engine light on. It starts up ok but after 5-20 seconds will start having the misfires with ESC light coming on. The engine light is always on now. Got garage to read out and came back with misfire on cylinder 3. I have replaced all plugs (NGK iridium) and leads but still persisted. Now I have also changed the coil pack with a new NGK U2003 and hoped that would work but no change whatsoever. What else can it be? My battery is not great I believe but car starts fine so not sure if it can be related?! If it’s nothing electrical I can only assume that the engine itself is causing it but an engine failure at 56,000 miles would be ridiculous right? Hopefully some can point me in the right direction! Thanks in advance.