The one thing we should start with is that the MB battery performance is heavily impacted by the outside temperature. I did a 5.4 mile trip on Saturday and only had 25% battery remaining at the end. That trip was in e-mode, because I knew the car should be able to do it without the engine on. It included some sub-30mph pottering for roughly a mile uphill, which used about 20% of the battery, an uphill acceleration to 60mph that used about 15%, a downhill cruise that gave me 2% battery back and a brief sub-30mph section that used a few % then the opposite journey to return home. There’s a good chance the same journey in hybrid would have not used the engine either. If you’re 100% confident your car can’t do this, there might well be a problem with the battery.