is my alternator going bad

hello, i have a 2001 CV and everything seems fine until i put it in drive and step on my brake the volts start to drop, with the car in park and headlights on volts stay the same and with AC on it stays the same, put new battery in last week other one was 4 years old and dead. will the alternator not charge with heavy load or is there something else i might be missing.

thanks

You will need to have the charging system checked for a proper diagnosis. It could be as simple as corrosion on a connection or a loose wire in the charging system. Good luck.

Bad ground somewhere? Check all the frame to body straps and grounde wires especially in the brake light circuit if your problem is when you step on the brakes.