lithium question

BFL13 wrote:
I saw this while Googling about the 12v battery--some confusion and also Tesla might be changing to AGM in newer model cars--anyway if this is correct, the 12v battery is a 45AH sealed FLA that is charged by the car somehow using an algorithm set in firmware at 14.4, but outputs to the 12v things at 13.4. The 12 battery gets recharged when it reaches some lower SOC at some set-point I think ???? Not a clue.

Looks like you want to get at that 14.4 the 12v battery gets and not the 13.4 from the camping outlets and 7-pin?

Easy to measure the voltage in the cig lighter with your digital meter.


"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"

Good find, and good info.

I just did a test using the model 3 (should be the same for the Y) and by configuring the HVAC to manual with heat and AC off, the total loss was 2 percent of the main pack in 6 hours. Much better than auto. Still a big loss for nothing over 24 hours but would work in a pinch, or at night when no generators are allowed etc. Of course it would be higher once the DC to DC converter is connected to the accessory port. But it’s max 9 amps at 12 volts so that’s only an extra kilowatt over 9 or 10 hours. Think I’ll order the victron tomorrow. 80 bucks and free shipping. Should be a fun project...that I’ll probably never use. :). Always fun to tinker.