1999 ML-430 Clicking sound
 

I tried to start my SUV this morning and all I got was clicking sounds. It would not turn over. I was able to start it yesterday no problem. Lights, gauges etc all worked fine so I don't think it's the battery. Where should we start looking for the issue? I've only had this vehicle for about a month so new issues are being uncovered now.

Thanks!

weak car battery, replace it

battery drain
 

Im working on her 1999 ML430, It has a large drain on the battery when voltage meter placed between battery cable and post reads battery voltage, I removed fuses one at a time and relays no drop, I tried disconnecting modules as well. I removed cable to altenator still drawing same. I removed power center covers found, I assume, battery cable coming from battery tested ohms ok, tested to ground, It has between 3-4 ohms. I do not have a diagram, but I assume the cable was getting this due to the altenator was still connected. but is that a straight shot from battery to power center terminal? I am just perplexed when cable is removed from power center the draw slowly comes down to 3-4 volts and stays there, like a capacitor. I guess she needs to take it to the dealer because I need wiring diagram.