It shows the battery start up voltage and the cars charging rate of the 12-volt battery. When the car is off it turns off.

Yes, that will only show the 12v battery when the car is 'awake'. But the problem with the 12v battery shows up when the car is off or 'sleep'. In EQEV, the car continues to draw from the 12v battery while in the OFF state, and the traction battery constantly charges and top-offs the 12v battery while the car is off. If this regular maintenance mode charging does not happen, then the 12v battery depletes the SOC while the car is asleep, ending up as a dead battery.

You will need a blue-tooth type battery monitor that will monitor the 12v battery SOC 24/7 like the one I have installed. But be warned, even with such device monitoring the 12v battery, it may be difficult to predict a sudden loss of charge from the 12v battery and the demise that follows. Though so far I have not experienced it yet.

 

When I first turn on the cat it shows a normal 13.7 volts which I believe the battery's resting voltage then I see it start to charge with a higher voltage. I am thinking it might show the battery is starting to fail if the starting voltage is 11 or 12 volts.

 

I really doubt your 12v resting voltage is at that high. Remember that car wakes up before you even open the door. You approach the car with a fob on you. A few feet away from the car, car has been awaken. At that point, the 12v battery is no longer at the resting voltage.

 

Well actually when I first get in the car and touch the break, I read 12.7 for a few seconds which is the same as the car battery resting voltage. I then see the voltage drop and climb.

While this approach is not nearly as sophisticated and complex as your approach I am seeing the same thing in real time.

 

I just did a quick experiment using the Bluetooth BMII battery monitor on my EQEV. I connected the app via Bluetooth and started monitoring the live voltage on the 12V battery.

With a fob in my hand,

1. I approached the car. 12.78V
2. The car door handle presented itself. 12.78V
3. Open the door and sit in the car. 12.33V
4. The car went through initialization steps and turned on the screen. 12.24V
5. The car is REDY 13.24V
6. Sitting in the seat, READY but parked. 14.09V

What you see on your monitor after sitting in the seat is the voltage at step #5 above. As you can see from the graph, the car has already awakened and had an initial draw from the 12V battery for the door handle presenting and initializing the car. In my case, the resting voltage, as shown above, was 12.78V from step 1 to step 2. As soon as the door handle presents itself, the battery voltage quickly drops, and the on-board DC-DC converter starts charging the 12V battery. The 12V battery voltage you are seeing is the initial charging level at around 13.2-13.4V. Then, depending on the battery's charge level, it will continue to rise to ~14.5V over the next minute. The charge remains at this level until the system determines that charging is no longer necessary. This can last anywhere from ~10min to half an hour, even if the car was turned off.

Here is the larger every 2-minute voltage log recorded. Since the recording was made every 2 minutes, it lost the initial dip that occurred during the live monitoring (steps 2-5). However, what the graph shows is that the resting voltage of the 12V battery remains at ~12.8V before the quick On-and-OFF and after charging has stopped. And even though the On-and-Off was done within less than 3 minutes total, and I was out of the car, and the car turned off by 3 minutes after the initial door presentation, the car continued to charge the 12V battery for at least 10 more minutes.

What you really want to monitor is the 12V battery charging cycle, to ensure that top-off charging is occurring while the car is in the OFF state, and the SOC voltage never drops below 12V while the car is in the OFF state. Checking the voltage after the car wakes up is a good idea to verify the charging voltage, but that is not what indicates a weak or dying 12V battery.

 

All that is monitoring is the voltage of the DC to DC converter that’s charging the 12v from the HV battery when the car is on. To really monitor 12v health you’d need a Bluetooth monitor that mounts under the hood and records historical voltage over time when the car is off. But 12v problems aren’t common so I wouldn’t worry about it…

 

All that is monitoring is the voltage of the DC to DC converter that’s charging the 12v from the HV battery when the car is on. To really monitor 12v health you’d need a Bluetooth monitor that mounts under the hood and records historical voltage over time when the car is off. But 12v problems aren’t common so I wouldn’t worry about it…

Agree, just one minor correction. Ultium has had MANY 12V system issues - countless dead Lyriqs and Hummer EV's in the early days. Also their ICE cars which shared similar module electronics in the VIP / Global B architecture. Car wouldn't sleep right due to issues from stuck software updates, internet comms, and coupled with bad software in the serial data gateway module.

It has gotten better, and perhaps they have it worked out now on Equinox EV. But calendar 2023-2024 was not a good time for many GM vehicles and 12V issues.

 

No fair using the forum Search feature. That's against the self-help rules, lol.