blessed_trades

I got a 13 c350 coupe and the main battery keeps dying when I keep the door open too long or play music with the car off, it has been diagnosed as a bad battery. My mechanic said that both batteries need to be replaced even though the one in the trunk is still good. I trust him since he is certified Mercedes tech but just would like to know if that’s the case since $950 cad for two batteries is a lot of money