Renault, Check Emissions light and failure to start?

Hi, my 05 Grande Scenic 1.6 (megane) has started to throw up problems in the past 3 wks, a warning light has come up "Check emissions" along with the symbol that looks like an engine since a power failure. It has failed to start - battery completely dead when I put in keycard in, tried both keys but the dash remained blank & car didn't turn over. Car was started using jump leads and ran fine - then 2 days later same again, except this time I couldn't even unlock the doors. We booked into garage but had to jump start it a 3rd time to get it up there...battery was replaced and dignostic check showed nothing, so computer was reset and I got it back...fine until next day - dead as a dodo again. Couldn't unlock doors, no power again. Called AA, new battery checked - minimal drain - can taken back to garage - fault showing on dash again. Electronics checked by mobile auto-electrician but nothing found. Car kept on forecourt for week, started each time that mechanic tried it (daily), so invited to collect it again tho nothing found. But same problems happened again 2 days after collecting it and the mileage counter may have jumped, also discovered window jerky when pushing button for it to lower. Car jumpstarted and taken to auto-electricians in town. Full check found nothing again and confirmed new battery was performing 'perfectly'. Computer / windows re-set. Found it a little heavy to press clutch when starting it to drive home...and it kept cutting out / offering to cut out as I edged out in heavy traffic, but I managed to rev it to keep going or keep re-starting it...but once I got to point of being able to drive more steadily it picked up and was fine. Am now very anxious each time I go out to car - I live in the country and have little baby with me all the time when trying to do other runs for older kids. Consultation with former Renault service manager didn't throw any light on this, he didn't know what prob could be if diagnostic checks didn't identify a fault. ANY ADVICE or help?? Am very nervous of paying even more money to get nowhere, fault still occuring and car unreliable, leaving my kids stranded, or me and baby. The auto-electrician said that renaults were an electronic nightmare since the time of the electronic keycards, which is a worry. I had a renault for 8+ years before and it was great...but also had two company vans which led to lots of problems with Dealer servicing & repairs even under warranty so have cause to doubt Renault's "expertise".