Cold weather battery drain (VCV already replaced)
 

After changing the vent control valve TSB on my 2009 G37x I’m still having problems starting the car in cold weather (-10 C / 14 F), and that’s not even when it’s really cold here (-25 C / -13 F)! After changing the valve the car worked fine while temperatures were around freezing (0 C). Once it got cold and the car wasn’t used for a week, the battery was at 4.2v. Using a booster the engine turned and started.

The dealership said there’s no ECM reprogramming required when I changed the valve. Another dealership reprogrammed the ECM 4 years ago when I brought the car in for the same problem but they didn’t change the vent control valve back then.

I have a Costco 640 CCA battery that’s a 2-3 years old and the dealership ran a battery check and said it’s OK. I use a 10A battery maintainer to charge the battery after it loses charge.

Can you help me get my car to start reliably?

First, I'd take the Interstate battery back to Costco while it's still under the 3-year warranty and get a fresh battery. Next, how about building a small thermal blanket around the battery?

I changed the battery for a new one, left the car outside in the cold (-10 C) for 6 days. The battery dropped to 11.90v and the car did start on the first try, with a little hesitation. We'll see if it holds