Hello all long read. The newest addition to our cars is a 2007 530i m sport 6 speed manual as far as I can tell it has pretty much every option available (heated front,rear,steering,big wheels etc) except the bigger screen like the m5s have. And it's owned by my father in law ha lucky guy. Anyways when the car was first bought at 157k miles it pulled very well no limps or shudders and power all throughout the revs. 5k miles later he gets hesitation and misfires so we change the plugs at home with my help and we change the individual coil that was missing. Easy right? 200 miles later the car gets another code. This time for a knock sensor. So a new oem bmw mini knock sensor is ordered and installed by his mechanic using new bolts all done as should be. When we get the car back there are no check engine lights or anything or hesitation jerking. But it doesn't feel as strong as before noticeable by me and him. later that week the whole dash lit up with DBC failure and abs light and cel I suggested it might be the battery but it never gave us trouble before so they didn't think it could cause this much havoc. So his mechanic spoke up and said that he recommended new plugs and a new plastic valve cover to replace his metal one that had some seepage? Which seemed odd to me because I've heard that the metal magnesium valve cover was more desirable on the n52? But again not my car not my money. So to me this guy is loosing all cred fast. But we get the car back and low and behold it's got body damage from his shop and all the lights are still on. Plus he crimped the valve cover seal while installing so now it's seeping again. Total fool. Plus new plugs. but all the coils are still the same while not new and not failing it's still better to just do the whole tuneup at once not so half done like he did. Anyways now completely stumped and fedup my father in law asks for my opinion and I say that he should check his battery. Low and behold it's a 4 year old h6 battery. Wrong size. Too small. It's surprises me how well the car ran for 5k miles with this battery pulling so strong. So we get rid of that and put in a new h8 size battery and have it coded and scanned at a popular German euro shop chain here in the south. They coded it and they said that dbc and all the other lights turned off but one code remained for a crankshaft position sensor which explains the long crank starts at times. 2 days go by and all of the lights are back on lol. Am I wrong or was the battery coding supposed to help? I know it's better for the battery life and alternator. My question is would the crank sensor cause all this?? I've also seen wheel sensors. But I'm pretty stumped too. Sorry that it's alot any help would be appreciated.