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Discussion Starter #1 (Edited)
Yesterday I sat my my 2012 Volt parked and turned the ignition to the "ACC" position (by holding the power button for 5-6 seconds without stepping on the brakes) so I could run my AC inverter to charge and play on my laptop while I waited for my wife. I also have the Torque App and monitor many parameters from the car, one of them being the 12V battery voltage.

I don't remember what the 12V battery was when I parked, but it was after a 30 minute drive (and this car is a daily driver) so I assume the 12V battery was fully charged, but after 30 minutes using and charging my laptop with the ignition on ACC, my 12V battery had fallen down to 12.1V and my AC inverter stopped working.

Nothing in the car was on except for the radio at a low volume and my laptop charger (which I assume was drawing 5-6A from the 12V accessory port).

I just read that the car has a 40A/hr battery, which should've gone a lot longer than 30 minutes before reaching 12.1V (which I figure to be 30-50% discharge on a lead acid battery according to this https://i.stack.imgur.com/B2gEX.jpg and many other graphs I found).

So should I replace it or am I wrong about some assumption I made?
 

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For the last 20 years, I always replace the 12 V battery when it is 4 years old. That strategy has served me well.

My experience is that after 4 years, the odds go up quickly that the battery will fail.

The Volt is no exception, just a different charging mechanism for the 12 V battery.
 

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Yesterday I sat my my 2012 Volt parked and turned the ignition to the "ACC" position (by holding the power button for 5-6 seconds without stepping on the brakes) so I could run my AC inverter to charge and play on my laptop while I waited for my wife. I also have the Torque App and monitor many parameters from the car, one of them being the 12V battery voltage.

I don't remember what the 12V battery was when I parked, but it was after a 30 minute drive (and this car is a daily driver) so I assume the 12V battery was fully charged, but after 30 minutes using and charging my laptop with the ignition on ACC, my 12V battery had fallen down to 12.1V and my AC inverter stopped working.

Nothing in the car was on except for the radio at a low volume and my laptop charger (which I assume was drawing 5-6A from the 12V accessory port).

I just read that the car has a 40A/hr battery, which should've gone a lot longer than 30 minutes before reaching 12.1V (which I figure to be 30-50% discharge on a lead acid battery according to this https://i.stack.imgur.com/B2gEX.jpg and many other graphs I found).

So should I replace it or am I wrong about some assumption I made?
50% discharge on an AGM shouldn't be DEAD, but it's getting down there. And it's possible that the assumption that you were only drawing 5-6 amps running the inverter to make AC to power a brick to make DC might be low, too. Laptop bricks are about 65% efficient, good inverters are about 85%, so ... it piles up. On top of a 4+ year old battery, that's not nothing. And I'm gathering that this isn't an unusual part of your routine. So, maybe it's time.

OTOH, for only 30 minutes? I'd just leave the car powered up. That HV battery has a HELL of a lot more power than the 12v, and a backup generator to boot. If using the laptop a thing you like doing, you may wish to just get DC-DC power supply for the laptop. Most manufacturers have a brick with a 12v car plug on it they'll sell you, and that'll probably get the efficiency of whole "car to laptop" power path up quite a bit.
 

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If any question, at that age, then replace it. I own an auto parts store and the number one creator of distraught people is dead batteries! Ralph7 has the perfect strategy!
 

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Forgive me for asking, but why put it into service mode when you could just have the car on as normal? I can see if your traction battery were depleted it might force the engine to turn on once or twice but it's not like you were sitting there idling and wasting gas for the entire time.
 

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Your title asks if your 12v battery is dying, and the answer is ALL of our 12v batteries are dying. My theory is go until it causes you a problem - then replace. I'm at 74 months with my OE battery and it still is doing it's primary job. The Volt battery is not the same as the "starter" battery in an ICE vehicle, it doesn't have a great deal of extra capacity. OTOH it is not in the nasty environment of an engine compartment and it really doesn't get heavily loaded in normal operation. Your use of "ACC" mode is not normal, so you shouldn't expect it to handle the task.

My vote is just leave the car on, unlike ICE vehicles it doesn't belch nasty exhaust at "idle" so no harm done.

VIN # B0985
 

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For the last 20 years, I always replace the 12 V battery when it is 4 years old. That strategy has served me well.

My experience is that after 4 years, the odds go up quickly that the battery will fail.

The Volt is no exception, just a different charging mechanism for the 12 V battery.
The Volt 12v battery is an exception in that it never has to crank a cold engine. What that means in this particular application might be a different question.
 

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In service mode, all car electronics are powered up including all engine computers, hybrid computers and body computers. Service mode is nothing like "acc" mode on cars that ignition keys.
 

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There is thread after thread after thread on this forum of sad stories of a Volt's 12 V battery suddenly dying and causing the owner some grief. The one common item - the battery is usually between 3.5 and 4.5 years old. Yours is living on borrowed time. Replace. Now.
 

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Has anyone figured out what the voltage number is whereby when the battery drops below the Volt will not start?

I've been looking into adjustable battery alarms that can be set at a specific threshold. If we knew the lower limit was, say, 12.3V, then an alarm set for, say, 12.5V might be worthwhile.
 

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Has anyone figured out what the voltage number is whereby when the battery drops below the Volt will not start?

I've been looking into adjustable battery alarms that can be set at a specific threshold. If we knew the lower limit was, say, 12.3V, then an alarm set for, say, 12.5V might be worthwhile.
Wouldn't help much. As soon as there is load the voltage will drop below the threshold.

Just leave the car on to do this work. And replace the 12v battery at the first sign of trouble or every 3 years from the born-on date. Batteries have a shelf life as well as an in-service life. They are additive death dates.
 

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As soon as there is load the voltage will drop below the threshold.
It is my understanding that the 12V Volt battery does not actually experience any load during starting, as would, say, an ICE car. And, that 12V battery failures are strictly a voltage threshold issue.
 

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I'd like to get some perspective on the 12V battery under the hood vs. the battery in the back hatch under the floor mat. What exactly does each do? It seems that the problems people experience, and when they refer to their 12V battery dying it's usually the one under the hood? I did do some searches to try and get more info on each battery, didn't find hits on the description of each batteries function. I did find a thread where the OP did say the 12V battery in the trunk was the one that went dead and caused error messages, dash warning light.

I also found a few owners saying they would pre-emptively replace the 12V battery (again, the one under the hood? Trunk? Both?) at 3 or 4 years, somewhere in that age range. An auto parts owner suggested that was a very good idea as he said one of the issues that causes car owners the most angst is a dead battery (ICE or EV). Interested to read any input/guidance that is out there, TIA.
 

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Forgive me for asking, but why put it into service mode when you could just have the car on as normal? I can see if your traction battery were depleted it might force the engine to turn on once or twice but it's not like you were sitting there idling and wasting gas for the entire time.
+1

A) Just turn the car on, it makes no difference except you've not got the traction battery energy available.... which will charge the 12V battery anyway once you start the car up, so basically all you've done is stress the 12V battery. You've done absolutely sweet nothing at all to 'save' any sort of electrical energy there, in fact probably used more of it.

B) So what if the battery drops to 12V under load? Sounds like it's in a good condition to me, to sustain that sort of voltage whilst running all the Volt systems for a half hour!!!

I don't think you have really understood the difference between an 'acc' mode in an ICE and what you have done here. Think about it a bit more and I think you'll realise you've done a nonsense thing here.
 

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There is only the single 12V battery in the hatch under the floor. No battery in the engine compartment.
I suspect there is confusion here with the boosting instructions in the manual referring to the remote positive terminal under the hood.
 

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I suspect there is confusion here with the boosting instructions in the manual referring to the remote positive terminal under the hood.
Yes, the above is true as well as the whole issuing of the terminal connector being installed at an angle on the 12V? under the hood. Those references to the cable being installed incorrectly I believe referred to the "12V cable connector" so that was also confusing. Freshcut's post makes sense. When I first got my Volt, I pulled up the floormat in the back, and looked at the 12V battery back there. The terminal posts under the hood I guess are just that, terminal posts but not an actual 12V battery.
 

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I think what you have proven is that your 12V battery is in excellent health. The fact that it was able to sustain the accessory load and the car's electronics for 30 minutes without dropping below 12.1V is admirable, IMO. It appears to have plenty of surplus capacity beyond what is required for normal use.

I recommend you not use service mode for running accessories, and your battery should last a good while longer.
 
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