So a light came on , on the instrument clutter that was red and had a picture of a battery and said visit workshop . Got battery and alternator tested . Said battery was good , just needed a char

the ESP is the "Electronic Stability Program". There's a bit of explanation and backstory here from Mercedes. (Which I found quite interesting.) There are a couple things you can check before resorting to a trip 1. Check Battery Voltage - the battery could be an issue. And if the battery is the original battery, it may be due for replacement anyway (after 8 years of use). So the a DC volt meter and check that the power between the 2 battery terminals (when the car is off) reads 12-14.5 volts. Anything less could create problems in theory. 2. Tire Pressure - Get an accurate gauge and check to make sure all tires are close (probably within +/- 2-3 PSI) to the factory spec on the label (assuming stock wheels and tires are installed). You will get some changes in tire pressure while driving, especially at higher speeds and stress levels (like bumps on the highway). Incorrect tire pressure reads could affect how the computer thinks it needs to work, and getting the tires in the right range could get it working properly again. Also if your tires are very worn, you may need to replace them as that could also affect tire pressure and/or traction control readings dramatically. 3. Brake Fluid - Make sure you have the appropriate amount of fluid as spec'd in your owner's manual. Bringing your fluid to spec could resolve the issue since it is a braking dependent system. 4. Brake Pad Wear - It may be hard to get a good angle, but try to see how much of the brake pad compound remains. If there are other indications (like the squeezing brake indicator) replacing the pads may resolve the issue. If none of those points are bad, or when corrected don't fix the problem after a day or two, then definitely take it to a shop.

How old is that battery? I just replaced mine because a few of the cells were bad.....though in theory u can charge it but it will not be at max Cold cranking amps(CCA)