The Hanhook 12V batteries in the Model Y/3 may not be AGM but it appears Tesla is charging them as if they were. I monitor the 12V post voltage with a Bluetooth voltage monitor. Anytime the car is awake the voltage is either 14.4V (actively charging via DC-to-DC converter) or 13.4V (DC-to-DC supplying power to 12V operational loads). Dropping to 13.4V did not happen until a fairly recent firmware update, prior to that it was always 14.4V when not sleeping. I purchased a NOCO Genius G7200 to maintain charge level, with the negative cable not connected, so the battery is not connected to the car while using the charger. The charge mode I use (or should I say the charger automatically selects) is 12V Cold/AGM. According to the NOCO manual the charge voltage in this mode is 14.8V (which is what my BT device measures). Neither Tesla nor the Smart Charger charge at 16V. If I am using the wrong charging mode, what mode should I be using? Note the BT monitor might be off by +/- 0.1V
From Hankook web page:
Charge for 24 hours as following voltage upon battery type.
- 12V MF Battery: 16V
- 12V AGM Battery: 14.4V
See this Hankook webpage for more info.
Battery Maintenance - Hankook AtlasBX Technical Information