A Class with ACS transmission Auto Clutch-less system) your cars are also fitted with this link so be aware, Chris however informs that on his ACS he lost 4th gear as well.
I realised that the garage must have pulled the fuse knowing that it would cause the engine check light to come on.
I reported the garage to the Trading Standard Office.
They said they could not act on it because there was no proof, but they said they would make a note of the garage address.
The battery should be recommended by the manufacturer for the Mercedes 'A' class, different models Diesel, Petrol, use different batteries so make sure you make the dealer aware of you vehicle details.
In addition as the battery is being fitted inside the car it should be fitted with a breather /vent facility, this is connected to you present vent pipe.