no power to Renault Grande Scenic - how can I fix intermittent fault?

I have an 05 Grande Scenic and 3 wks ago I went to start it but had no power - display lit up faintly then nothing and engine didn't turn over. I tried both electronic keys. No hint of a prob before that. We jump started it and a warning light came up on dash, but car ran fine. Was alright next day then happened again...no power to dash or ignition, unable to even unlock doors. I've had the car well over a yr, without a hint of a problem at all...then suddenly - hit with this. After the 3rd time of having to jump start it, we got it into garage and battery was replaced, followed by diagnostic check which found no prob and the computer was reset. All fine taking it home - but next day dead as a doughnut again...wouldn't even unlock. Phoned garage, and called out AA - taken back to garage tho AA check showed minimal drain on battery...mobile auto electricial ran tests on car a few days later...nothing showed up at all and each day the car started. Mechanic spoke to ex-head of servicing for Renault in Edin, but he had no idea of possible cause...nothing he could suggest to check so I was asked to collect...thought the brakes were squealing a bit, but overall, okay....next day - completely dead again. Each time the dash is completely clear - not even clock continues. Mileage overall may have jumped but not sure about that...After another jump start, car taken to a auto-electricians, but nothing showed at all on their checks. Battery 'near perfect with lowest drain he'd ever seen". Electric window found to be a bit jerky, but it was re-set before checks on machine and afterwards Computer was reset again...so then was asked to collect and take home. Started driving, brake/clutch to start seemed a little heavy on starting and car very quick to cut out initially, going out into heavy traffic....re-started each time tho and revved car to try to keep it going, by the time I got to point where I could turn bk to garage it had started to run better....brakes def squealing on way home, not dreadful but noticeable and slight smell / hot on drivers side (front wheel) - don't know if there is any connection or not.
Steering felt fine, wipers and lights were working to best of my knowledge. With a baby and 4 other children, living in the countryside - an unreliable car is my worst nightmare....we also just don't have money to pay for more costly repairs or trade in car, so I'm desperate for some help....any ideas?