2008 Mercedes-Benz C300 stability control problems

Approximately a year ago my c300 locked up on me would not start. I had it towed to the mercedes dealership and when they check it they stated that eis was out on it. The cost of the repair was over $2000.00. About two weeks ago, as I started the car in the morning for work I noticed that the start was a little hesitant, so I replaced the battery and things got back to normal. Today leaving for lunch I placed the key in the ignition and turned it to get the "slient click" again.

On january 2,2015 went from home to a retail store with no issues. After a few minutes at he store went back to the car, open de door, lights on, control panel on, car will not start. Put key on ignition switch, dead, will not make any sound. Used different set of keys, nothing, car dead. Call the dealer for advice, was told to replace the battery or jump start the battery. Called my tow, did jump start and nothing, call dealer was advise to replace the battery.