Renault Megane

You'll find that Renault recommend almost everything to be done by a dealer, then steal your wallet for the privilege.

I'd suggest you lift that cover thingy that is over the engine and take a look for yourself. My 07 Megane would take about 5 minutes for a battery change. (Same as my wife's 52 Megane)

anywhere good will change the battery for you at a nominal price, I would not suggest diy any longer due to the faults and problems you may induce by battery disconnection. the system should remain powered up through the whole change procedure, for this you really need three power supplies: the original battery, the new one and an extra one to maintain the power.

Costco for instance charge 2 pounds on the cost of the battery for fitting.

Mrcheerful