Can anyone help pls.?
 

The other day when we had the snow storm my ml350 battery light came on so i went an replace the battery but i'm still having problems with it not charging still i thought it might be the alternator so when i got it running again i disconnected the positive cable and it keep on running it didn't cut off but the volt meter say it was low can anyone give me a idea of what is going on with it not stayin charge

Sounds to me like the charging circuit is working - just not optimally.
What is the voltage on the terminals across the battery with the engine running?
If you've got the terminals disconnected, what is the voltage on them not connected?
Have you verified that all your grounds are clean and tight?

Do your tests with a separate volt/ohmmeter.

I was told that i need to replace my alternator which seen to have gone bad and not shutting off when the i turn off my car. And was draining my battery