This is incorrect. The Model Y monitors the voltage of the 12V battery when the vehicle is parked. Even when not plugged in, when the voltage of the 12V battery drops below a specified voltage the Tesla will power on and charge the 12V battery. You can reduce how often the Tesla vehicle must charge the 12V battery while the vehicle is parked by leaving Sentry mode, Summon and Smart Summon turned off at your home location.When a mobile tech was installing homelink onto the MY. He was telling me all about the components under the frunk. He mentioned to me that the 12v battery does not get charged when the MY is plugged in. He said it only charges when the vehicle is on and being driven. I thought it was strange. He said some people put a trickle charger on the 12V when they park it for an extended period. Can anyone confirm that's actually the case?
All during Covid lockdown my Model Y sat in my garage, most of the time unplugged, unlocked and with Sentry mode turned off at my home location. The Model Y would wake up about every 24 to 30 hours. I was aware of when the Model Y would wake from sleep mode because of the Alexa Auto device plugged into the 12V accessory port. Whenever the Tesla Model Y powers on the 12V systems the Alexa Auto device would communicate via BT to the Alexa App on my phone. The Alexa app then creates a notification that it is ready to drive.
If what the Mobile Technician said was true then you could never park a Tesla vehicle for any length of time before the 12V battery would discharge and you would be unable to unlock or wake up the Tesla vehicle to drive. This is not the case. If you read the Tesla Model Y Owners Manual there is no mention of connecting a 12V battery tender to the 12V battery if you leave the Tesla vehicle parked, not driven. The Owners Manual states that you should leave the Tesla vehicle plugged in so that the vehicle can charge the lithium battery pack as needed. The Tesla vehicle automatically maintains the charge of the 12V battery.