Mercedes-Benz of Pompano

When you buy a Mercedes, I guess you plan on paying more for service. I own (bought new) 2 Mercedes in LA and began having them serviced at Mercedes of Pompano. One is a C350E plug in hybrid. In February the hybrid system stopped working. They replaced the auxiliary battery. A month later the battery mulfuncrion light started coming on. The dealership can’t figure out what it is but they want $2,000 to run diagnostics and if it is the hybrid battery $27,000 to replace it. The warranty on the battery is 6 years or 50k miles. I bought the care late April 2018 and it has 47,000 miles. Despite having a warranty book that came with the car that says the battery is warranty for 6 years or 50,900 miles, the dealership says that the battery warranty was only 5 years. They recommend I just sell the car. Am I supposed to lie to someone and sell them a problem car - that shows the ethics of this dealer. Never going back to them and will be selling both Mercedes (with full disclosure).