"That a 100 amp alternator will not charge a dead battery."

Got up this am, car battery dead. Jump started it to make a doctor's apt. Drove around for an hour first and when I come out battery is dead as a mackerel. (I brought along a spare yellow top just in case).

Advance Auto's test computer says the battery is just discharged. My diagnostics reveal that my alternator puts out 14 volts and that there aren't any parasitic discharges on the system with the engine off-my diagnosis, battery shot and I may have to buy another one anyway. I'm charging it now to see if they can get a positive test afterwards.

I ran into this once at Autozone years ago and finally just had to buy a new battery after I couldn't convince them.

 

Sometimes a really drained battery will revive after a slow trickle charge when a quick charge like running the engine will not do the trick. Have had this happen myself.

 

Could an accessory be draining the battery? In both cases, the car sat unattended for a length of time.

 

Pretty sure your alternator s/b a 140 amp unit in the SS, I know it is in the Z28. Also a 100 amp will charge a battery in any condition. If the voltage at the battery terminals is 14 Volts then the alternator is putting out. Make sure the voltage stays there if you turn on the headlights w/engine running.. Sure looks like you have a bad battery to me. A dead battery should charge up, but could be damaged by a total discharge at times. After running what is the voltage at the terminals with engine off, it s/b 12.1 or so. Should not drop below 9 volts when cranking if in good shape, maybe down to 8.0 if marginal to getting old. I have been told a lot of BS by AZ when my old battery would charge up fast but go dead after 2 seconds of cranking, or running the radio w/o engine on for about 10 mins. They tried to sell me an alternator, said battery was fine, I walked away.

 

i just had pretty much the exact issue. back in october replaced a faulty alternator and knew the battery was bad or gonna be shortly. advance told me the battery was fine it just needed a charge, the battery was far from dead and had no problems starting the car. fast forward to a couple weeks ago. drove 15miles ran into store for 5 minutes came back out and car tried to crank over but very slowly and wouldnt start. got a jump and car ran fine but noticed on occasion whether battery was warm or cold sometimes it barely would turn over. went back to advance and the battery came back as bad when they tested it. picked up my new battery today and all is good again.

so in other words i dont put a lick of faith in what advance(or prolly any other parts stores) testing machines say. plus whats with the price of batteries. they have doubled in price in 6 years,

 

Trust me, I noticed. I finally got fed up and bought the cheapest 1 yr. battery I could get just to get some reliability. It was about the same price that I paid for the 3 yr., 3 years ago.

 

Last fall I had to move a car that had not been moved in a year, batter was under 2yo car did have a LED switch that drained the battery HARD given the amount of time. It was hard to even jumpstart the car, ran it with a raised idle for 20 minutes, 3 days later it wouldn't even crank. A trickle charge later and it is fine sitting for 30days between starts even with the LED switch draining the whole time.