i have 1984 300d with 330k miles on it. My battery is 4 years old and it a autocraft silver from Advance Auto.

While using the ac this Summer, my battery seems to losing power. My car was slow to crank over yesterday so I drove about 10 miles to the store without the AC or stereo on.

When I left the store, my car started right up without hesitation. When I drove home, I turned the AC and stereo on. When I pulled into my driveway, I shut my car off. I then tried to immediately start my car but my battery would not turn the engine over. It seemed to be completely dead but my dashboard coil light would come on.

I had the battery tested at Advance Auto and they said the battery failed their battery test. It was only putting out 632 cca and the battery is rated for 850cca.

I am going to buy a new battery today but I was wondering if I also have an alternator problem.

Shouldn't the cars electrical system run completely off the alternator and not use any battery power while it is running?

Any thoughts?

Thanks.

Pete