Charging system issue?

Since I had the car, the battery light has been on. Two batteries were replaced, one in trunk and a new one from Benz under the hood. When I check the voltage in the trunk it shows 14 some under the hood 11 some, is that possible? If I leave the car running, no issues, then when I turn it off and come back 2 days later it starts. Then after that if I leave it linger it is dead. If I jump it I will start but only if I jump it from the rear battery.