I know this is an old post but Ive just read it to find a solution to my recent problem.
Stop/Start error keeps coming up on the display and I can't turn the stop start off.
My battery is 3.5 years old and is wearing out and so needs replacing. On the stop start Qashqai when the battery is not fully charging the ECU on the car automatically puts a higher charge into the battery. The error message then comes up on the display. I looked around for an AGM 096 replacement battery. You need to get an AGM type of battery for any stop start vehicle. I went to Halfords and purchased their own brand for £145 with a 4 year warranty + £25 for fitting.
The only reason I paid for them to fit it is that you need to reset the ECU to let it know you have fitted a new battery. If you don't reset the ECU the car will keep charging at the higher rate and overcharge/burn out your new battery in a shortish period of time.
It's not the cheapest battery but a 4 year warranty is quite long and it's easy to take back to Halfords if it fails within the warranty period. If I bought a cheaper battery online it would be harder to send it back and would need to find a garage to reset the ECU. As it was it took Halfords 15 mins maximum to have the car back running perfectly. Peace of mind.