Many of us are having the same problem. There is nothing wrong with your 12V battery. My 5 y/o battery still holds a charge just fine, even if I replaced it thinking it was bad. The new 3G TCU gets locked 'on' downloading certain data. It remains active until the 12V is dead.
There is a workaround. In your "Carwings" setting in the car:
1. Disable data sharing with Nissan
2. Remove all saved charging locations
3. Disable downloading of data
Essentially, anything that connects to Nissan to download data programmatically needs to be disabled.
With the above done:
- You can still update charging stations manually if you wish. Know that there are phone apps that could serve this purpose better as they show chargers status, history, rating, etc.
- You can send commands to turn your climate controls on/off or program a timer for it.
- You can see your battery charge status
- Your trip data can be retrieved by the mobile or web apps.
- You can still upload your vehicle's data to Nissan if you set it to "when the car starts" (or something like that)
- You can command your car to start charging
- You can send Google Maps addresses to your onboard navigation system
So, overall, not too bad of a compromise. Your battery will no longer drain but the 3G TCU is still crap so once every few months you may lose connectivity to your car. If that happens you can either "pull the fuse" (search this forum) or simply disconnect one of the 12V battery terminals for a few mins to reset it.