07 Pontiac G5 won't start after temperature gets below 40 degrees

I had issues last winner that whwn the temperature gets below 40 degrees the car would not start, put a battery pack on it for half an hour would start up right away. I’ve already replaced the battery with a new one. I was thinking it was the alternator but why would it be the alternator cuz it wasn’t doing it at all this spring and summer it started doing it soon as it got cold again

Did you check all connections to the battery? are they clean and tight?

Yep. If they werent clean wouldnt I had issues during the spring and summer time as well?

Then something is draining your battery. First thing to check is the dome light.Make sure its off after you exit the car.

We already went through all that last winter. I even disconnected the battery overnight hooked it back up and still the same thing

What is the voltage of your battery and cold crank amperage?

It’s only sitting at 7.5 :expressionless:

And cca is 615

So basically, dead…

Yep. :unamused: I just don’t know what would be draining it.

Haven’t had any issues with it until today too.

You need to run a parasitic drain test. Check out a video on how to do that from Eric The Car Guy on YouTube.

Suspect aftermarket car alarms and aftermarket stereo systems, especially amps.

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Good advice above. A basic voltage test at the battery terminals is worthwhile too. Before first crank of the day the battery should measure about 12.6 volts. Immediately after starting the engine it should measure 13.5-15.5 volts. If you are getting different numbers than that , post them.