[LarryO]

So, there are a number of reports of 12V battery problems. I had a similar problem yesterday, but I think it may be the charger. I had driven my Bolt in the morning and returned home about noon. At about 5PM I went out to run an errand and got the Conditions not Ready for Shift. This was followed by numerous additional error messages. The car would also not shut off. After a few minutes of this the dash went black and the car was mostly unresponsive.

I checked the 12V battery and found it to measure about 7.5V. I put my 10A charger on the car for about 2 hours. At this point the car powered up and worked normally. When I started the car, the battery came right up to 13.8V and the electronics pump was running. It appeared the on-board charger was working.

I left the car sit overnight without plugging it in. The battery voltage was a bit low at 12.1V but it only lost several mv overnight.

I'm at a loss as to what happened. I think the battery should have had a pretty good charge at noon since the car is driven fairly often and when not being driven is plugged into the OEM charger at 240V. How could it be dead 5 hours later?

I'm wondering if the charger just stops working for some reason. Possibly the battery was almost dead at noon?

Today I took the car to the dealer. They checked the battery and pronounced it good. There were a bunch of codes set that were thought to be due to low voltage. Otherwise, everything was fine.

They did perform the N222369400 recall, HPCM 2 reprogramming, ADS improvements.

This made me wonder if some of the 12V battery stuff was actually some bug that caused the 12V charger not to work intermittently.

At any rate, just passing this along FWIW

 

[ARCowboy]

Hm... could also be some some kind of parasitic drain. Do you have any aftermarket accessories hooked up ? Specifically to the negative of the battery ? Since the car uses a hall effect sensor on the negative of the battery to judge SoC and variably charge the battery.

 

[jefro]

Not easy to look at a battery connection and see if it is good. May have to remove and clean?

 

[LarryO]

Hm... could also be some some kind of parasitic drain. Do you have any aftermarket accessories hooked up ? Specifically to the negative of the battery ? Since the car uses a hall effect sensor on the negative of the battery to judge SoC and variably charge the battery.

No accessories. There could be a parasitic drain, but it would need to be something the car is doing. It would need to come and go too since it looks pretty reasonable when I measure it.

 

[LarryO]

Not easy to look at a battery connection and see if it is good. May have to remove and clean?

Well, it looks brand new. I have had it off several times to reboot the car and it looks perfectly clean.

It was pretty weird that the blue light strip was on when I first entered the garage. The garage was dark and no other lights were on. Maybe the headlights did not turn off? I keep them on auto.

 

[ARob]

@LarryO Since the recall SW updates on the HV battery, many owners have observed a small amount of power continues to be pulled after the Target Charge is reached. This appears to be 12V battery maintenance and diagnostics.

I wonder if it might be worthwhile to plug in nightly for a while and see if the 12V stays charged?

I am 4.5 years in, 83K miles and have never had 12V issues. I plug in nightly with very few exceptions.

 

[LarryO]

@LarryO Since the recall SW updates on the HV battery, many owners have observed a small amount of power continues to be pulled after the Target Charge is reached. This appears to be 12V battery maintenance and diagnostics.

I wonder if it might be worthwhile to plug in nightly for a while and see if the 12V stays charged?

I am 4.5 years in, 83K miles and have never had 12V issues. I plug in nightly with very few exceptions.

I plug in nightly too. I use departure charging most of the time. This particular day it was not plugged in the night before nor when it died. I'll have to keep an eye on the battery voltage.

I suppose that a large load like the headlights on could draw it down in 5 hours. I don't know why it would be doing that. Of course, this could be easily missed since the lights do come on when you shut the car off. I would not normally check to see that they timed off normally.

 

[ARCowboy]

No accessories. There could be a parasitic drain, but it would need to be something the car is doing. It would need to come and go too since it looks pretty reasonable when I measure it.

You have a hall effect/amp meter for your multimeter ?

Any idea how old your battery is ?

 

[EV Engineering]

While charging in hot garage or using air conditioning While seating for extended periods of time Bolt will have temperature under the hood over 160°F that will negatively affect 12V battery SOH. I have done some testings with some Bolts and all suffer from this problem if vehicle is not in motion. If there is no other way but charging in hot garage, make sure your front end of vehicle is facing garage door. And if necessary crack open garage door a little so Bolt has access to air from outside of garage, and if necessary keep hood ( bonet) open so you are not killing your 12V battery because BMS has to use air conditioning to cool down big battery pack. This little things matter if you want to have 12V battery for long time.

 

[LarryO]

You have a hall effect/amp meter for your multimeter ?

Any idea how old your battery is ?

Not a clamp on just a series connected shunt meter. I just short across the shunt until the car settles down to a low state.

The battery has seen a tough life and I would not be surprised to see a problem with it. The car was built 8/18 and sat for 14 months until I bought it 12/19. It still looks to be performing fairly well but I'm sure it has lost capacity.

I don't know how it was tested at the chevy dealer. I think they may use a transconductance tester. At least that's what GM specified a few years ago.

 

[Greenfan]

I suspect departure charging could result in a low 12 v battery due to the extended 12 v charging at the end of the propulsion topup charge I see ,never tried departure charging ,could 12v charging happen before hv charge?

 

[LarryO]

While charging in hot garage or using air conditioning While seating for extended periods of time Bolt will have temperature under the hood over 160°F that will negatively affect 12V battery SOH. I have done some testings with some Bolts and all suffer from this problem if vehicle is not in motion. If there is no other way but charging in hot garage, make sure your front end of vehicle is facing garage door. And if necessary crack open garage door a little so Bolt has access to air from outside of garage, and if necessary keep hood ( bonet) open so you are not killing your 12V battery because BMS has to use air conditioning to cool down big battery pack. This little things matter if you want to have 12V battery for long time.

I would like to do it better but so far, I have to live with charging in the garage. What I have been doing to help mitigate this is to use departure charging with an early AM completion. At least doing this the garage temp is lower than it might be. I had planned to add some ventilation but have not gotten around to it.

The situation is a little worse with the newer software since the car never did battery cooling after charging on my low-rate charger. Now it does run for a while. Most of the time by morning the garage is below 90F. I do wish the cooling air was not vented through the motor compartment.

At any rate, whatever degradation is present would make it easier to run down due to an unexpected load.

 

[ARCowboy]

Not a clamp on just a series connected shunt meter. I just short across the shunt until the car settles down to a low state.

The battery has seen a tough life and I would not be surprised to see a problem with it. The car was built 8/18 and sat for 14 months until I bought it 12/19. It still looks to be performing fairly well but I'm sure it has lost capacity.

I don't know how it was tested at the chevy dealer. I think they may use a transconductance tester. At least that's what GM specified a few years ago.

You could probably manually turn the headlights on for 5-10 seconds to take off the top charge as well.

I would expect more than 4yrs of life out of an AGM battery personally. After 5.5yrs, the AcDelco H8 AGM in my diesel colorado was still showing 12.4-12.5v after sitting at least overnight, sometimes for a couple days.

 

[ARCowboy]

Are you one of those people who leave their keys in their car in the garage by chance ?

 

[LarryO]

Are you one of those people who leave their keys in their car in the garage by chance ?

Nope.

The OEM AGM in my Camaro is about 6 years old, and it still seems ok.

 

[EV Engineering]

Onboard DC-DC converter is way more than traditional alternator. It has multiple different types of charging scenarios. But in one case it cannot stop 12V battery SOH going bad if it is seeing many times 160°F+ temperature under the hood. If possible opening the hood while charging or using air conditioning for extended periods of time seating still is better than nothing.

 

[LarryO]

Onboard DC-DC converter is way more than traditional alternator. It has multiple different types of charging scenarios.

Actually, some of the newer GM alternator systems work in a similar way. My 2016 Camaro with an AGM battery does. Obviously, the engine needs to be running. I'm not sure when they started this or how many models do this.

 

[EV Engineering]

Actually, some of the newer GM alternator systems work in a similar way. My 2016 Camaro with an AGM battery does. Obviously, the engine needs to be running. I'm not sure when they started this or how many models do this.

2005 is when they started using this on ICE vehicles, but onboard DC-DC converter is much more smarter.

 

[Sean Nelson]

I checked the 12V battery and found it to measure about 7.5V.
...
This made me wonder if some of the 12V battery stuff was actually some bug that caused the 12V charger not to work intermittently.

If the battery got down to 7.5V then I'd consider it suspect. It may charge back up to over 12V, but whether it has any actual capacity or not is another story altogether. You'd need to do a load test to evaluate its health, not merely measure its voltage.

It's important to understand that the 12V battery maintenance algorithm in the Bolt is limited in its intelligence. It will charge the battery if it detects the voltage is low, but it merely does so at specific intervals and only for fixed amounts of time. It won't do much for a marginal battery that's been abused.

 

[LarryO]

If the battery got down to 7.5V then I'd consider it suspect. It may charge back up to over 12V, but whether it has any actual capacity or not is another story altogether. You'd need to do a load test to evaluate its health, not merely measure its voltage.

It's important to understand that the 12V battery maintenance algorithm in the Bolt is limited in its intelligence. It will charge the battery if it detects the voltage is low, but it merely does so at specific intervals and only for fixed amounts of time. It won't do much for a marginal battery that's been abused.

Well, the dealer blessed the battery as "OK" My minimal tests look fine. However, for some reason the battery was dead 5 hours after the car was shut off. Just prior to this, it was driven about 15 miles. It is normally plugged in while not running. I would expect it to have been fully charged when it was shut off.

That leaves three questions in my mind;

1) What could I have done to run the battery dead in 5 hours or less?
2) Has the charger has not been working correctly if at all for some period of time?
3) What unexpected glitch caused this?

Unfortunately, after charging and reboot, all seems perfect now. I am hoping that possibly the recent software upgrade may have addressed this.