Timeline of events so I can keep things straight and for your entertainment.
Update: 9-01-2017 Finally got car back and hopefully is fixed now.
Late April or early May (exact date not recorded); 12v dead and needed a jump start.
May 08, 2017 thru May 12, 2017 Car at dealer for warranty replacement of charge port LED ring (1st quadrant no longer illuminated)
May 18, 2017, Car sends text message 12v is low, 12v dead and needed a jump. It measured 7 volts prior to jump starting. Traction control went nuts took car to dealer.
June 19, 2017 Dealer called said car is ready. (out of state until Tuesday 6/20 so can't pick up)
June 19, 2017 Car sends text message 12V is dead. Called dealer and let them know.
June 20, 2017 Attempted to pick up car. Dealer didn't charge battery.
June 21, 2017 12v battery charged and car ready. I suggest let it sit overnight to make sure battery isn't dead next day since that's partly the reason I brought it in in the first place.
June 22, 2017 12v battery is not dead. Pick up car from dealer.
July 12, 2017 Parked car at approx 1pm at 5:20pm battery is down to 8 volts. Accidentally clear all DTCs when using ODBII to read DTCs.
July 14, 2017 12v battery is dead, parking lights left on. 12v battery charged overnight.
July 15, 2017 DTC codes read several indicate low 12v. Battery Drain Check performed, measured 20mA (50mA max). Battery tested with digital tester. Impedence measures 5 mOhm, est 534 cranking amps.
July 24, 2017 Car parked after lunch. Shortly after 6pm 12V battery is dead, car is jumpstarted and battery is charged overnight.
July 25, 2017 Car dropped off at dealer for 12v battery issue.
Aug 07, 2017 Car picked up. Dealer can't find any problem. Drove car several times, battery never went dead.
Aug 11, 2017 12V battery is dead again (7v). I also discover that Passenger door lock sensor doesn't work.
Aug 14, 2017 Drop off at dealer to fix door sensor and see if they can determine anything about 12V battery going dead.
Aug 18, 2017 Pick up car. Dealer forgot to reconnect lock sensor when performing door lock recall. As expected, no faults found with the 12V system.
Aug 25, 2017 12v Battery is dead again, Jumpstart, drove home, drove to dinner and back home, then removed fuse for hardwired dash cam just to prove beyond any doubt it is not a source of power drain, finally, plugged in to EVSE about 50% on HVB. Realized I haven't been getting text messages from car since Aug 12. And locate my car indicated in MFM showed my car at a location I was at briefly on the evening of 8/19 so apparently telematics module stopped communicating. MFM app said last update was 2 days ago (8/23)?
Aug 26, 2017 After charging HVB overnight 12V battery was dead when I went to go to lunch. Jump started and went to lunch. 12V still dead after lunch jump started and drove home.
August 28, 2017 12V still dead as expected. Jump started and drove car to dealer. MFM is communicating with the car so apparently they are working on it.
August 29, 2017 I received a message from the car that the 12V is low. So at least communications with the car are working again. Talked to the dealer they were finally able to observe a high current draw from something related to wireless??? I didn't catch what it was. New parts ordered and expected to arrive 8/30.
August 30, 2017 New parts installed car and in theory all is good. Dealer is keeping car overnight to observe if excessive current draw on the 12V battery has been eliminated. Will pick up 8/31 if all goes well.
August 31, 2017 TCU is drawing excess current too. Ordered a new one.
September 1, 2017 The original draw down test was OK they let it sit overnite and the 12V battery went dead. They charged the battery and found 1.7A drain that went away when the RFA module was disconnected. Then they repeated after replacing RFA and found 0.4A drain from the TCU. Draw down test after both were replaced was 20mA well below the 50mA max. Hopefully this is the end of this story!
September 2, 2017 After putting my 12V on the battery charger overnight it was steaming sulfuric acid. After cooling down My battery tester showed 180 cranking amps and 13.34V. I figured the battery is surely toast now so out of curiosity I just kept using it until it would no longer start the car.
September 6, 2017 12V battery was strong enough to operate locks but not strong enough to energize HVB contactors.
September 8, 2017 Dealer replaced 12v battery under warranty. old battery tested at 170 cranking amps 12.8v. Hopefully the end of this story.
November 1, 2018 12V battery stone dead in the am. Jump started and drove to work. Car started fine at lunch but was dead again after work. Jumped car to drive home and charged HV battery and then put 12V battery on a 12V charger.
November 2, 2018 Used car all day, charged in the evening. No issues.
November 3, 2018 car parked with 77% high voltage battery SOC.
November 6, 2018 12V battery too low to energize contactors. Put 12V battery on 12V charger. Performed a draw down test. 1.35A load found on 12V battery. Pulled BECM fuse F11 and battery load dropped to 7.5mA. Reset fuse F11 and perform another draw down test. Battery load is 11mA, well within the 50mA maximum spec. Unhooked 12V battery and charged it up overnight.
November 7, 2018 performed another draw down test. 1.32A load on 12V battery, needed to leave for work so no time to verify it was BECM again. Attempted to hook 12V back up and drive. Got "yellow wrench see manual" error followed by "depleted battery" error with red battery icon and 0 miles shown on Guess-O-Meter. No ready to drive icon. Car previously parked with a 77% charge. Plugged in EVSE and car estimated 4.5 hours to charge. Charge completed in 45 minutes. GOM indicated 1 mile range. Car turned on and I got green ready to drive indicator. Miles on GOM slowly climbed eventually making sense with battery charge left. Performed a 3rd draw down test with same results. Went to check mA draw with F11 pulled and blew mA fuse on meter by inadvertently activating rear hatch button so no accurate mA measurement is possible.
November 8, 2018 Discovered that pulling F11 fuse while car was on is what causes the false battery depleted error. As suspected car will not charge with F11 fuse pulled. Verified F11 (BECM) is the cause of battery drain. Shut down car, put ammeter inseries with battery, pulled F11 fuse, 40 min. later no measurable current draw (ammeter can't read below ~100 mA due to blown fuse in meter). Scheduled service appointment.
November 12, 2018 Car sat unused with F11 pulled over the weekend. 12V battery measured 12.35V and battery tester indicated 8.6 mOhm. Dropped car off at dealer.
November 21, 2018 Picked up car from the dealer. They found the TCU as the culprit for the current drain and couldn't recreate BECM (F11) as the cause. Not sure why but after the first draw down test 1.3A current didn't go away untill pulling fuses 1-11. All tests after that I only pulled F11. Maybe pulling F11 caused the TCU (F1) to stop pulling current? Operating car without TCU (F1 pulled). Will see if 12V problems continue. Performed 1 draw down test with F1 pulled, measured ~10-12mA draw (using old analog meter that I severely question its accuracy).
October 12, 2019 Almost 11 months with F1 pulled and absolutely ZERO instances of a dead 12V battery. Installed low voltage disconnect to the power supplying the TCU.
October 18, 2019 Almost a week and no 12V problems.
Spring 2020 One instance of dead 12V battery. I think it was due to the door module misbehaving as the window wouldn't work right for a couple of days then the 12V battery went flat dead. I thought it was a broken window switch but after charging the 12V back up it worked fine again.
April 14, 2021 Replaced the OEM battery with a deep cycle LFP battery aka LiFePO4.
From original Aug 22 post:
I was thinking if the next time it happens I could hook up a good 12V battery / amp meter and then disconnect the cars dead 12V battery and see if it's still drawing current. Somehow accomplishing all that without breaking the connection between the battery(ies) and the car. But I'd imagine either opening up the door to pop the hood or the fact that the voltage got down to 7V would "shut down" whatever was drawing current. There were some good ideas in this thread
on how to monitor/data log the 12V but it seems I would almost have to leave my hood popped and have some way to alert me when the current draw doesn't drop after 40 minutes. In order to determine what is randomly drawing the battery down. I'm open to anyone's thoughts or ideas. I'm grasping at straws here. I also find it odd that I no longer get a text message telling me the 12V is low.
March 16 2018 12V dead after sitting at the airport for 3 days. Battery charged with HVB for 1hr 40 minutes, drove 45 minutes and charged with HVB for 1hr 50 minutes, Drove another 30 minutes and charged HVB to full in 3+ hours. So 12V should have been fully recharged.
March 18 2018 12V down to 11.5 V after sitting for about 24 hours.