battery clock

Hi, I need to replace the battery on our c200 205 series (with stop start) and wanted to know if the lack of power during the short changeover will result in any issues such as radio, clock settings being lost, or indeed anything more series. I know for our CLC 203 series, changing the battery...

I left my car (W212 e350 blue efficiency) at airport for 3 weeks. On my return battery was completely flat - key would not even unlock door/boot. (And no I had not wittingly left anything on) Had to get car jump-started which it readily did and everything burst back into life. However I now...