Charging problems i drive the one time down the track and the car is hard to start back

That is definitely wrong, not normal. Voltage should stay at 14 volts or near that until the battery is close to fully charged, then will slide down to about 13.5 volts, and stay there while engine is running. Also, a fully charged battery should show about 12.6 volts at a minimum, especially a new battery.
I don't know what is going on with your system. Take it back to Merc- were they aware of how it is acting, voltage-wise? Doesn't sound like it. One small possibility: is your alternator belt not tight enough?

Use a volt meter or test light, disconnect the negative battery cable from the battery post. If the meter reads 12 volts or if the test light is lit start pulling one fuse at a time until the meter reads zero or the test light goes out.

Make note of what circuit the fuse protects then start working your way back from there. It cold be as simple as a dome light being left on but you need to narrow down where the problem may be located.

I hope this helps, good luck!

it is your air idle control valve witch is located on the back of the throttle body..

Contact your dealer as they have the equipment to track down a fault like this

check the alternator, If it starts with new battery but ten k`s down the road wont start again, then it has to be alternator not charging.

Oh dear one of these problems. Sound like a loose plug or dirty connection in plug Very hard to find Start by checking battery and ignition circuit plugs and terminals Hope this helps Feel for you!

I am guessing you have power windows. Happens to mine sometimes.
Slam the door a couple to few times, see if that doesn't put the window back on "track". I mentioned this to the dealership a while back and they were going to charge about $90 to pop off the interior part of the door and put it back on track. They said it "builds up dirt".
I actually also toggle the window switch a few times to see if it will move slightly and then do my door slam thing a couple to few times. I seem to get this problem when it rains.
I hope it helps.

First check what caused the problem. If the window was hard to put up and down then clean the running rails either side move the window up and down with your hand to make sure it is moving freely then just glue the window back to the track with glue recomended for it

you have a short in the steering colum

this is most often caused by a defective engine wiring harness, it gets breaks in the wire inside the wires insulator, very hard to track down, bend the harness where it goes to the engine, see if u Can make it act up.