Intermitant starting problem?

Last week i noticed that i had a headlight bulb out on my 2007 Megan. I tried to replace it myself and which then seemed to cause a bigger issue. I had the door open while replacing the bulb and then while trying to start the car the car would not turn over at all and the break went very hard. I called Renault and was told it was the battery and if i got is started tio give it a good run and it would be ok. I did manage to start it with a set of jump leads. Gave it a good run and then for the next week it was all fine (no rain all week by the way) This weekend I was out and had been to a few shops and it was fine. I start my car fine put the roof down drove no more than 500 yard to get petrol. I did leave the key / radio on while I paid and then when i tried to start the car it wouldn't start. By managing to put one foot on the break and the other on the accelarator i started. I went to my local garage who i have used for year and they were stumped. They think it is something not switching off when i lock it and leave it although this does not explain why it was ok for a week. Again today I had the same issue and needed a jump start to get going. The battery was new last June so not even a year old and also had a charge of 12.45v and an ok green light on the display. Due to the confusion they suggested I got to a car electrical specialist or take to renault but previous experiance tells me that it may be something that is not as bad as either may tell me only because there seems to be "features" in renaults that are not commanly known to those who do not own one. Top me it seems that if the car is left with the radio / key in the car / lights on for any amount of time then it won't start without a jump. Any help / suggestions would be appreciated