car is getting harder to turn engine over on 2003 Mercedes-Benz C240

when getting in car this problem is getting worse over time i maybe noticed wow car not cranking right away may 2 or 3 months ago but turn key sounds like not getting gas then vrooom... replaced battery this summer i am getting worried it will strand me what can it be?

Asked by for the 2003 Mercedes-Benz C240
"hard starting" is usually not a battery issue, but you need to confirm that the alternator output is okay. even if the check engine light is NOT on, you still need to see if there are any stored codes. plugs need replacing at 100,000 miles; fuel filter every 60,000 miles. also, is it hard to start on both a cold and hot engine??
My car is doing the same thing. I was told by an authorized dealer that I had a bad coil which needed to be replaced and a complete tune-up which they wanted to charge $1000 for. Price in unreasonable. Probablu does need the coil.Hope you have better luck than I.