Redvers

I have a CLK230K 2001 model. I have never had any problems with it until the last couple of weeks. The car was idle for six months as I was travelling a lot. When I tried to start car a couple of weeks ago the battery was flat. I arranged to have the car picked up and serviced (B) and MOT'd. Everything was fine and the battery was fully charged. The battery is only a year and a half old and within 3 year warranty. Garage said that battery was tested and is fine. I picked car up on Christmas eve and suddenly the boot would not open remotely. I tried the key and it snapped. I used WD40 and now the barrel just goes round and round. Decided I could live without the boot over Christmas and drove to Swansea. Three days later I drove back to London. Nearly 500 miles round trip and all fine. I didn't drive the next day but the day after I could not start the car. Battery flat. I called Breakdown and they came and started car with jump leads. Mechanic said that the alternator appeared fine. Drove around and later in the evening the car would not start again. Had to get Breakdown out again and get jump started. Mechanic suggested a dodgy earth wire. I now have jump leads as this is only way to start car. Did book in to garage but snow this week caused that to be cancelled. Any help will be appreciated.