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Discussion Starter #1 (Edited)
A common misconception is that the 12v battery will be kept charged as long as the car is plugged in. Like many things about the Volt, the answer is "sometimes".

Plugged In Does Not Always Mean 12v Battery is Being Maintained

Even if the Volt is plugged in, the 12v battery is only charged when the main 360v battery is also actively being charged. This mean that after the main (360v) battery is fully charged, the 12 v battery will NO LONGER be charged even if it starts running down. So simply having your Volt connected to a 120v or 240v charge cord (EVSE) will not prevent the 12v battery from running down when stored for long periods of time.

Parasitic Drain of 12v Battery Even When Plugged In
Basically, when the 12V battery is connected to the car its State of Charge (SOC) will gradually run down if it is not occasionally charged or otherwise maintained. This is because a normal parasitic drain of as much as 25mA occurs even when the car is OFF and completely "asleep". So after 30-40 days this could cause your battery terminal voltage to be too low and require either a "jump" (under the front hood - see owners manual), or a period of charging prior to using the car.

Should You Worry About Storing for a Few Weeks?
No. If your car will be sitting for a few weeks under normal conditions, don't worry. It will be fine. A month or more is another matter, as would be extreme temperature conditions.

Will Cold Weather Damage the Battery or Make it Undriveable?
No, and maybe. Cold temperature will not damage the battery, but long-term storage while unplugged in arctic temperatures could cold-soak the battery to such a point that it would need to be plugged in to warm the battery befor the car could be driven, with or without the ICE. See more in this post later in this thread: http://gm-volt.com/forum/showthread.php?18435-Long-Term-Storage-Guide&p=3670402#post3670402

FOUR LONG TERM STORAGE METHODS
There are four methods that can be employed when storing the Volt for extended periods longer than a few weeks:

1. Transport Mode. This is used at the factory to put the Volt in a kind of hyper sleep for long shipments overseas. Transport Mode may also be left on while the vehicle is in dealer inventory. So it would seem the same could be done for those who store their Volts for a few months.

2011-2013 Vehicle Procedure

To turn the Transport Mode On:
1. Start the engine
2. Activate the hazard flashers
3. Press the brake pedal
4. Press and hold the Start/Stop button (if equipped) or turn the ignition key to the crank position for 15 seconds"

To turn the Transport Mode Off: Repeat the procedure above.

2. ScottF's "Off Peak" Scheduling Trickle Charge Trick. As discussed above, even if the Volt plugged in, the 12v battery is only charged when the main 360v battery is also actively being charged. Given that ...

  1. Run the main battery down. O miles left is best.
  2. Plug into the "slow" 120v charge cord (supplied with the car).
  3. Set the Volt's charge scheduler to recognize only Sat and Sun as allowable charge days by telling it to only charge off-peak and set those days as "off peak".
  4. Set the charge timer to 15 minutes.
Now the car will *want* to get charged (it's empty), but it can charge for only 15 minutes each day for only two days a week (30 min/week total).

While the main battery is being charged, the 12v battery will be topped off too. Because the car takes 10 hours to fully charge using the slow charge cord at 12 amps, you could keep the car and it's 12v battery "trickle charging" like this for 20 weeks of vacation (10 hrs/.5 hrs per week = 20 weeks). At week 20 the main battery will be fully charged and the 12v will no longer be maintained by the main battery charging system. It will be on it's own and slowly drain.

Of course, selecting the 8 amp instead of 12 amp charge rate will drag this out further. The 8 amp level level takes about 14+ hrs. to fully charge the Volt's main battery from empty. So that would give you about 28 weeks (14 hrs/.5 hrs per week = ~28 weeks = ~7 months) of storage before the main battery is completely charged and the 12v battery is on it's own again.

3. Battery Disconnect. This is the method detailed in the Owners Manual. Open the rear cargo hatch. Remove the 12-volt battery black, negative (−) cable from the battery to keep the 12-volt battery from running down.

In addition, to avoid potential damage to the high voltage battery, perform the following recommended steps:

• Store the high voltage battery with 1/2 charge or less.

• Always store the vehicle in an environment between −10°C (14°F) and 30°C (86°F).

• Vehicle storage at extreme temperatures can cause damage to the high voltage battery.

Reconnect the 12-volt battery when ready to drive the vehicle.

4. AGM Trickle Charger. This method is alluded to in the Owners Manual in the battery disconnect method. Use a battery trickle charger intended for use with an AGM (Absorbed Glass Mat) type battery. From the June 2011 GM Tech Link: "To properly maintain the 12 volt battery while displaying the vehicle, use a battery maintainer, such as the EL-49642 (a Midtronics PSC-550S, about $450 new). The charge voltage should be kept below 14.8 volts due to the Volt having an AGM battery. "

In addition, to avoid potential damage to the high voltage battery, perform the following recommended steps:

• Store the high voltage battery with 1/2 charge or less.

• Always store the vehicle in an environment between −10°C (14°F) and 30°C (86°F).

• Vehicle storage at extreme temperatures can cause damage to the high voltage battery.

What happens if I come back and the 12v battery is dead?
If the car won't respond to your key fob, don't panic. Despite your best attempts (above), the 12v battery has drained down.

Flip out fob's metal key and use it to unlock the door. Pop the front hood. On the (North American) driver's side, toward the steering wheel, locate the gray, bare metal hexagonal ground post. To it's left is a black plastic box with a cover. Pop the cover to expose the thin, threaded positive post. Use these to jump the Volt. To avoid damaging the radio, other electronics, avoid injury/death, or otherwise cause damage not covered under your warranty, read the complete details and cautions in your owners manual under the Jump Starting section.
 

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Automatic Stickie.

Automatic FAQ entry.
 

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From the Owner's manual:

Remove the 12‐volt battery black, negative (−) cable from the battery to keep the 12‐volt battery from running down or use a battery trickle charger.
If I connect the $450 trickle charger to the 12V battery, leave the 12V battery connected to my Volt, and plug my Volt in to my EVSE, will the TMS keep my HV battery safe in 100+ degree Texas weather indefinitely?
 

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From the Owner's manual:



If I connect the $450 trickle charger to the 12V battery, leave the 12V battery connected to my Volt, and plug my Volt in to my EVSE, will the TMS keep my HV battery safe in 100+ degree Texas weather indefinitely?
I'd like to see a picture of this $450 trickle charger! I have one I keep on one of my vans I rarely use, but it was about $30.
 

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I propose another method for long term storage:

Lend Volt to a friend or a schedule of multiple friends. Upon returning, send GM a bill for word of mouth advertising :)
 

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The only thing that sticks in my mind is:
Having 2 sources of power on the cars 12v system, from two different 120 or 240v sources may create a floating ground thru the cars 12v wiring and the charge circuit.

I may be wrong, but had this happen more often with computer networks becoming floating ground points between buildings.
 

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Has anyone else stored their Volt in non-climate controlled storage? I'm going to be out of the country for a couple months this summer, and up here in Wisconsin it shouldn't get above 30 C for any length of time, but I'm still a bit nervous about damaging the battery...
 

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Has anyone ever verified that suggestion #2, scottf's trickle charge scheduling using small off-peak charging windows actually works? For which model years? Preparing to go on a short trip (that likely doesn't need any precautions at all), I tried experimenting with this technique. What I found is that if you shorten the off-peak window enough, at some point the car basically says "screw this, you don't have enough off-peak time, I'm just going to start charging right away" when you plug in. Like if it can get full charge in 2 days it'll work as expected, but if full charge is longer than that it just overrides and charges in non off-peak. Nice theory but doesn't work in practice?

From my 2012 manual:
"Also, if the selected electric rate settings result in a very long charge completion time, the vehicle will start charging immediately upon
plug-in. For example, if the electric rate table is setup with all “Peak” rates and the rate preference is to charge during “Off-Peak” rates only, then the vehicle will start charging immediately upon plug-in."

Personally, I'm going to disconnect the 12v if I ever go on some really long trip without the Volt.
 

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Wondering about Transport Mode

Looking further into Transport Mode as a possible long term (1 - 2 month) storage solution:

An email from a GM Electric Vehicle Advisor said:

The only way that we have found that would allow you to safely transport the vehicle without having to disconnect the 12v battery would be Transport Mode.

You will first need to discharge your high voltage battery to 50% charge. Then you can activate Transport Mode ...
Then there's this post, which says battery saver (aka transport) mode can work up to 70 days.

Battery Saver Mode: Page 5472 in Volt/Ampera Service Manual

The battery saver mode reduces the parasitic load of some modules during overseas shipment or during vehicle storage conditions. This improves the drain time on the battery (up to 70 days without the battery going dead).
So I left my 2014 Volt unplugged in Transport Mode for 6 days. On return, I measured 12.63v on the battery, which was exactly what it was before I first started fooling around turning Transport Mode on. Unfortunately I didn't record the electric miles remaining before I left, so can't say whether the HV battery was used to maintain the 12v charge.

Does anyone know if 12v charging happens in Transport Mode? Or if thermal management happens?

Any advice before I try this on my next month-long trip?
 

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I was a little nervous about Transport Mode, but I ended up using it for 3 months last summer while I was out of the country. When I got back I didn't have any issues, it started right up, the HV battery was at the same charge I left it at, and it immediately started running the engine for EMM.
 

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Transport Mode worked fine for me over a 33 day storage.

Initially: 12v battery measured 12.61v, 17 miles EV range.

After 33 days in Transport Mode, 12.52v, 17 miles EV range.

Maybe someone has a more definitive figure for the AGM 12v battery, but from a glance around the web this looks like about a 10% reduction in state of charge. That would be consistent with the 70 day figure cited by Volt Gambler.
 

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I can verify that the trickle charge method using 30 min/week of off-peak charging did Not work on my 2014 Volt. Which agree, the manual warns of. I had 92% charge (so it knows it doesn't need much), set up the off peak scheduling for 15 min Sat/Sunday, and plugged in. Volt chirped it's horn 4 times (first time I remember that), and started charging, big green light solid on, and indeed taking it's L1 1000W. Maybe if I play with a longer weekend charge times....

I have been using delayed charge to charge in the early morning, not because of lower rates, but because of temperature. Here in Austin, it seems like we can go weeks and weeks with the temperature not going Below 86F (not really, but it seems that way in July and August!).

I would certainly like a mode where the car is plugged in (for cooling ability), but charging disabled. I do have overseas trips a few times a year, when I am away for 2 weeks at a time. I really don't want to leave it plugged in all the time with a 100% charge in the heat. I did that for 1 week just last month (like the manual says), but did worry about it. Of course, it was fine, but even so, this is just a software feature I'm asking for. With all the Peak, Mid-Peak, Off-Peak programming, they couldn't just add a Disable?
 

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I have taken my 2012 Volt cross country several times. I left it in New Mexico in October of 2013 for about 6 or 7 weeks. When I returned in December, it started fine, but got a check battery system message, which turned out to be a coolant low situation. I have looked through the manual table of contents several times, but found nothing about leaving it for an extended period, so I just leave it plugged in thinking it will take care of itself - after all the car wants to do everything else on it's own without owner intervention.

So this time I left the car in the garage plugged in for 5 months. I am now in deep do do it appears. Once again the fluid is low in the battery system, but the 12v battery is dead dead. I cannot open the hatch to get to the battery. I tried charging it at the connection under the hood, but the battery is not taking anything. The car is not in a position to jump it from another vehicle.

The GM advisor now tells me that on page 10-26 there is a procedure for long term storage that is not referenced by the table of contents. The nearest dealer that might be able to do something is 3 hour drive away. Now after digging I find that the car being plugged in does not charge the 12v battery, but it uses the 12v battery to keep the drive battery cool. Boy GM really needs to add some protection for that 12v battery - not just telling owners to fumble around disconnecting the 12v battery. How many people who live in warm climates use an air conditioned garage? What happens if you go to the airport and leave your car at long term parking anywhere in the southwest - you will exceed 86 degrees. I love the idea of running for a plane, but having to get out and disconnect the 12v battery first.
 

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Update 1 - Just jumped the dead 12v battery in my 2012 Volt. The engine started, so I thought I was home free. Here are a few notes:
1) My drive battery is fully charged, so the car decides it does not need to run the engine, so it shut itself off (12v still dead)
2) The systems all go to default mode, so lights on, radio on, climate control on. So all those who say shut this stuff off - good luck, the car wants them on. If it was locked when the battery went dead, the alarm system will go off. I had to use the manual door lock key to shut it off.
3) It appears that if the hood remains open, the car will remain running, so this may be a way to get the 12v battery charged.
4) As many have said - the 12v battery is only charged by the drive battery's DC to DC converter when the ignition is on and there is enough strength in the 12v battery to run the computers. So maybe once it started it will keep going on the DC to DC converter, but I think that is pretty risky proposition to close the hood and take off.
5) I have also read, and can verify, that as the 12v battery goes dead, all kinds of codes are generated from various sub-systems. I know if there is any codes from the battery cooling system (runs on 12v) it may disable the drive battery. It is hard to say what will be disabled.

So if it starts, leave it sit with the hood open, and maybe the lifeblood of the volt will return. Everything except the wheels needs the 12v battery, but they put very few measures in place to be sure it stays alive and well (like a charging circuit for when it is plugged in).
 

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Discussion Starter #19
Update 1 - Just jumped the dead 12v battery in my 2012 Volt. The engine started, so I thought I was home free. Here are a few notes:
1) My drive battery is fully charged,

3) It appears that if the hood remains open, the car will remain running, so this may be a way to get the 12v battery charged.
If the hood is open there are reports that it will charge the main battery to some degree, but only if that battery is not full. The 12V will get charged in turn by the main battery. But if the main battery is full, it won't charge with the hood open, and therefore neither will the 12V. That's my untested understanding.
 

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Very cold temp storage?

In Steverino's article #3 battery disconnect he says:
• Always store the vehicle in an environment between −10°C (14°F) and 30°C (86°F).

• Vehicle storage at extreme temperatures can cause damage to the high voltage battery.
Would storing a Volt at very cold temperatures damage the high voltage battery? For example, go on a trip leaving the Volt at home or flying out of some nearby airports where temps could reach -20F, stay below 0F for 36 hours, or stay 10F or below for a week. Over a period of a month, it might be average 20F, be rarely above 32F and get occasional cold snaps.

The most likely scenario for me would be trips two or three weeks away; could this damage the hv battery?
What about being away for months in the winter?
Would it be advisable to store it in a heated garage? At what storage duration should it be in a heated garage vs outside in the cold? At what temps do you have to start to worry about this? From comments by Canadian members, very cold temps are OK when used normally (daily or almost daily).

PS Is it considered more polite on this forum to start a new thread rather than resurrecting two year old thread? Thanks.
 
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