r/NissanMaxima

I have a 2010 nissan maxima and was sitting since last jumped for almost 3 months and i jumped it again 4 days ago, was running smooth until today. I had to jump start again and kept it running for 1 hour. Turned off, battery died again, jumped again and its on while i am typing this. I used a multimeter to see the voltage and it showed 8.8 while turned off. I turned the car on and it kept jumping between 18.3, 17.7, 19.2, 19.98, 16.5, 17.5

I googled and am sure this is not normal and seems to be a bad alternator. But reading more online also tells if the alternator was bad my car will stop even after I jumped and wont keep running.

Any input or advice will be appreciated as to what to do next?

Edit: changing the battery fixed it. Voltage while car running is between 13.4 & 14.6 now.

I foolishly bought a used Nissan maxima with 142k miles in it. The Carfax must have omitted some history and I brought it to my mechanic who is telling me tons of stuff needs to be replaced. I figured bare minimum I needed to replace tires, brakes and rotors. But engine mounts? Shock absorbers, the springs are busted as are the struts. The exhaust pipe is all rusted. There are error codes for the transmission, so I don’t know how much that’s gonna cost me. Do I have any recourse at all or am I stuck with this lemon? The mechanic said it looked like the car was in an accident which was not on the carfax. Anyone have any useful advice?