2001 Chevrolet Monte Carlo - Won't take a charge

My car will not take a charge. I can’t seem to see what the issue is after I charged it for 15 minutes, turn the key to start and it dies. Few months back, I had a mechanic charge it up and start it all up for me and it was up and running, but after he took the clamps off and closed the hood it stopped running. So I went on and did what he said and bought a new battery. A month later it died and now I’m in the same issue as before. What could be the problem after I cleaned the terminals and charged up my portable jump starter?

Likely a bad alternator or bad wiring. You said you had a mechanic. Did he check voltages to see what was happening? Did he check battery cable resistance? Did he do anything but shrug his shoulders and tell you to buy a new battery?

My advice is to to gt a better mechanic. If you own or can borrow a voltmeter, or even if the car has a voltmeter. Jump the car and then read the voltage on the gauge, if it isn’t close to 14 volts, the alternator or alternator wiring is bad.