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Discussion Starter #1
Today, tried to start my Bolt, after a two day rest, and it showed up with error messages. The key one was the 12 V battery symbol in red. Also said it was in battery save mode. This is my second experience with this phenomena. So I quickly checked the 12 V battery voltage (Vb) with my multimeter and it read 9.5 volts. I have been here before, so I put a battery charger on it and monitored the voltage. In 10 minutes the voltage read 13 V. That cleared the errors and I was able to “start” the car. At that point the voltage across the battery read 15 V. All OK except the Service Needed signal lit up. Took it for a 10 min ride and after shutting down, Vb read 12.6 V. Two hours later. tried to restart, same symptoms, Vb 9.68 V.
Hour later, before trying to move shifter, or brake position, it was in battery saver mode and Vb was 9.68 V. It allowed me to hook up the EVSE, set the charging time to immediate and began charging the main battery at 7 kW. Vb read 13.4 V so it was also charging the 12 V system.
I have a service scheduled in 3 days, assuming I can get it going and drive 50 miles to the dealer. The main battery is at about 80%..

Possibilities.
1. The 12 V battery is failing
2. 12 V charging system is messed up
3. Something is draining the 12 V system
I am guessing # 1.
Your thoughts and analysis are welcome.:(
 

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OEM 12V batteries are terrible. At least that's been my experience. I've had multiple ones fail prematurely. And a couple of those were supplied by GM.
 

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Sounds like either you have a bad battery or something is draining it while it's off.
Make sure you don't have a map light turned on. You'll need to test the battery too.
 

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Discussion Starter #4 (Edited)
Sounds like either you have a bad battery or something is draining it while it's off.
Make sure you don't have a map light turned on. You'll need to test the battery too.
Since it is under warranty, will see what the dealer can do. If it wasn't, I would probably replace the battery first and see if that fixes it. (TV repairman approach when TV's had tubes.) As I understand with AGM (adsorbed glass mat) batteries, you can't open them to measure the charge state of a cell with a hydrometer. Having a lead acid 12 V battery in a BEV with a 60 kW hr lithium ion battery seems like a strange system, but GM probably saves some money that way. It seems like they could have an emergency override, so in case of 12 V battery failure, it could switch to use the main battery for these tasks. Just sayin'
 

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Sounds like either you have a bad battery or something is draining it while it's off.
You could disconnect the battery's ground terminal and test it 12 to 24 hours later to see if it's holding the charge. That would eliminate or confirm the possibility of some sort of parasitic drain.
 

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Sounds like either you have a bad battery or something is draining it while it's off.
Make sure you don't have a map light turned on. You'll need to test the battery too.
don't the interior lights turn off after some amount of time? even if you have the switch on?
 

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Since it is under warranty, will see what the dealer can do. If it wasn't, I would probably replace the battery first and see if that fixes it. (TV repairman approach when TV's had tubes.) As I understand with AGM (adsorbed glass mat) batteries, you can't open them to measure the charge state of a cell with a hydrometer. Having a lead acid 12 V battery in a BEV with a 60 kW hr lithium ion battery seems like a strange system, but GM probably saves some money that way. It seems like they could have an emergency override, so in case of 12 V battery failure, it could switch to use the main battery for these tasks. Just sayin'
ALL cars require a 12 volt battery. Everything in the car is 12 volt dependent except the propulsion system, the heater element and the AC compressor, on this car. All the controls for these systems use 12 volt power. The 12 volt battery is what allows the HVB contacts to open to turn it off and close to bring the HVB online. Without it, you get nothing and this is all due to safety from the high voltage system. There has to be a way to shut the system off and a way to disable it to work on it and in case of a crash.
 

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don't the interior lights turn off after some amount of time? even if you have the switch on?
It should shut down with the battery saver system, but it won't power off before the system see's
enough voltage loss to activate it. He said the system notified him it was in battery saver mode.
That's usually a sign that something is left on to drain the battery and force battery saver mode.
 

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ALL cars require a 12 volt battery. Everything in the car is 12 volt dependent except the propulsion system, the heater element and the AC compressor, on this car. All the controls for these systems use 12 volt power. The 12 volt battery is what allows the HVB contacts to open to turn it off and close to bring the HVB online. Without it, you get nothing and this is all due to safety from the high voltage system. There has to be a way to shut the system off and a way to disable it to work on it and in case of a crash.
Right, and for system efficiency it's best to have a regular 12V battery which is a buffer between the APM (Accessory Power Module - the HV-12V inverter) and the rest of the system. The 12V load is quite variable and having the 12V makes syncing the load the source much easier. Plus the reasons you mention which is you need the 12V to boot the rest of the system (possibly even the APM and other inverters which may need 12V rails to run the controller).

Second time I've heard somebody wonder why the 12V isn't Lithium Ion either, answer is because it doesn't need to be. Saves quite a bit of money and easy to replace (not that it will need it, the 12V is very lightly used). To go Li Ion there would require some OEM special battery you had to get from the factory, and since you don't discharge it much the Lithium doesn't give you any advantage.
 

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AGM batteries are superior to lead acid. All the controls modules are 12 volt powered.
Same as all cars and trucks. An EV isn't any different.
 

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Discussion Starter #11
It should shut down with the battery saver system, but it won't power off before the system see's
enough voltage loss to activate it. He said the system notified him it was in battery saver mode.
That's usually a sign that something is left on to drain the battery and force battery saver mode.
In this case, I am sure nothing is left on, but the battery is failing to produce 12 V and that is what triggers the battery saver mode. My guess is that one of the cells is not producing much voltage for very long. It is very clear from what I observed that when the voltage drops below 12 V, it goes into battery saver mode. If you try to operate the parking brake or the shift lever, all kinds of error messages come up.
 

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Discussion Starter #12
AGM batteries are superior to lead acid. All the controls modules are 12 volt powered.
Same as all cars and trucks. An EV isn't any different.
Strictly speaker AGM batteries are just a subclass of lead acid batteries. They still use lead and sulfuric acid, it is just how the structure of the cells is arranged. They are supposed to be lighter, better and more expensive than classical lead acid. Probably doesn't mean that can't fail in the short term.
 

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Discussion Starter #13
In this case, I am sure nothing is left on, but the battery is failing to produce 12 V and that is what triggers the battery saver mode. My guess is that one of the cells is not producing much voltage for very long. It is very clear from what I observed that when the voltage drops below 12 V, it goes into battery saver mode. If you try to operate the parking brake or the shift lever, all kinds of error messages come up.
Of course, if the Bolt system is leaving something on to drain the battery down to 9.5 V and then the battery saver mode kicks in, that would certainly reproduce the behavior. I may try disconnecting the battery leads to see what happens. Not sure what that will do to the computer system and all the data though.:(
 

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Discussion Starter #14
One more question. Does anyone know the amp hour rating or other details about the Bolt OEM 12 Volt battery? I know it is small and AMG, but not its ratings.
 

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It would be interesting to find out if anyone switches to Lithium battery for their Bolt.

I remember an engineer talking about choosing a normal automotive battery over a different type just came down to cost, but other batteries were lighter and better. Especially since the Bolt doesn't need the CCA.
 

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Of course, if the Bolt system is leaving something on to drain the battery down to 9.5 V and then the battery saver mode kicks in, that would certainly reproduce the behavior. I may try disconnecting the battery leads to see what happens. Not sure what that will do to the computer system and all the data though.:(
This isn't a good test or idea. If you disconnect the battery you might cause the problem to stop.
If it's a module that's having a problem, removing battery voltage will reset it and possibly correct
the issue. I would do a parasitic load test before any battery disconnect. Then again, it might fix it! >:)
 

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interesting. Just opened my front hood for the first time to look at the 12V battery. Wanted to see if it was the old GM battery with the green indicator in a sight glass. Nope. Surprised to see that the battery is made in Germany.
 

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One more question. Does anyone know the amp hour rating or other details about the Bolt OEM 12 Volt battery? I know it is small and AMG, but not its ratings.
It's a 50 AH @ 520 cold cranking amps. An yes, the battery saver is designed to active at
a low voltage threshold. So, it's also possible that it could be activated by a failing battery.
 

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It's a 50 AH @ 520 cold cranking amps. An yes, the battery saver is designed to active at
a low voltage threshold. So, it's also possible that it could be activated by a failing battery.
lead acid batteries are around 2 volts per cell. Old six volt batteries had 3 cells and you can tell by counting the fill ports. 12 volt batteries, before they started hiding the fill ports or sealing them, you could identify by counting 6 fill ports on the top. When one cell goes bad, you lose a multiple of two. So when you see a voltage of something slightly less than 10 volts under no load, you've got a bad cell. Once that one cell goes bad, pretty much it's game over for that battery.
 

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Discussion Starter #20
This isn't a good test or idea. If you disconnect the battery you might cause the problem to stop.
If it's a module that's having a problem, removing battery voltage will reset it and possibly correct
the issue. I would do a parasitic load test before any battery disconnect. Then again, it might fix it! >:)
A forum user sent me the portion of the service manual on the 12 V system and its interaction with the HV battery is indeed complex. If the Bolt is off, the system checks the 12 V battery system from time to time and will use the HV system and inverter to recharge the 12 V system. It also runs in a desulfation mode. Too complex to summarize here, but this ain;t your 65 Mustang system for sure. In grad school my Mustang had a low battery and to start it hot didn't work because the compression was too high, so I used to let it cool for 15 min and then it would start! Worked that way for a few months.

On Star sent me the following warning today. "A critical issue with the engine and the transmission has been detected. Please service your vehicle immediately." (Yikes) So other than trying to get it started for a 50 mile ride to the dealer in two days, I am not messing with it.
To be continued.****:eek::eek::eek:
 
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