I recently bought a 2000 E320 sedan and have had several issues. On new years eve, I bought a brand new battery when the car wouldnt start and immediately found out it wasnt the battery. Today, as I started the car, I heard the battery struggling to start it but it did. I drove 20 miles, parked the car and 5 hours later it struggled again. I drove 10 miles, ran in the store and the same thing happened. I made it home and 30 minutes later, the car would not start. The lights are strong, the alarm system is working but it appears as if the battery is completely dead. There were no messages or codes appearing on the console and others claim that a message appears if the battery or alternator is bad.

Can anybody please point me in the right direction ?

Thank You