I think this may need to be replaced on my car as the battery keeps going flat, and there is no other obvious explanation. Anyone have any idea of how much this will cost to replace?
Thanks for these answers. The battery was checked 2 weeks ago as it was flat when I came back from holiday. There was a fault with the alarm siren, which was replaced but now it is flat again and I am wondering whether it just isn't charging. It is with the dealer at the moment but I was interested in what they would be likely to quote if this is the problem. I just can't afford to keep shelling out and can't do the work myself.
Thanks for all your answers. It seems that the radio may well be the culprit even though it recently stopped working. As the dealer already had the car to assess the initial repair, and I paid them for it, I don't intend to pay them again. Not sure they know that.

The dealer should be able to quickly test battery and alternator. General parts such as these are cheaper elsewhere and any garage can do the job. But there are obscure things such as radios draining batteries over a few days which can happen to various cars. Don't pay the Merc dealers £117 an hour labour charge for simple jobs. Any motor factor in Yellow Pages will give you a price for a new alternator on the phone for comparison purposes if necessary.

www.1stchoice.co.uk is definitely the best option.

well a new one costs bloody fortunes as with any Mercedes parts, but if you are looking for secondhand or reconditioned then here's a website to get in touch with www.1stchoicespares.co.uk its a website for about 250 second hand spares dealers you just register and add your details i.e make of car model and reg and they either email you or text you direct with the price I,ve used them loads for various bits for the cars I sell now and then hope that sorts your problem Big Mac

Are you sure its the alternator - battery could be bad. Same problem happened to our A140. Turned out we needed battery and alternator - continued flat battery due to poor charge rate can kill battery. The alternator was about £90.00 and the fitting about £50.00 (though this was not at an MB garage.) Quick Fit or similar can change battery at reasonable cost. Try and find a local garage who will work on these cars. many will and the hourly rate is less than half MB rate.
Where did you park when on hols ? If at an airport, close to runway, the planes can trigger your alarm on a regular basis.

You are professional.