[jon8491]

'19 Bolt, 12 days old w/ 55 mi on odo. I generally drive 2-4 mi/day.
I've read a number of threads here about the unfortunate circumstances of some users w/ their 12v battery.
I do plan to get the proper trickle charger for this battery but have not yet done that.

So I have been measuring my battery voltage for the last week and frankly, it has me concerned (I acknowledge I probably am over reacting....).

My concern is what may be a parasitic drain and if I don't charge often enough I will find a dead 12v battery. Originally I found the My Chevy iPhone app waking the car up whenever I got close, even with no intention of using the vehicle. I fixed that issue within the app settings. It is the only thing I have found that might be a drain (but bluetooth & perhaps wireless devices apparently remain active in the background). I'm not subscribed to OnStar but who knows what their equipment is doing when the car is off. Maybe even GPS is searching for a signal that it can't find. I do not use remote start. When I exit the vehicle, in a short time the DIC turns off and I don't see anything else going on.

Last week I charged for the first time (at 8a) to see how it responded. The HV batteries were at 87% and I charged to 100%. That brought the 12v battery from 12.58v up to 12.94 (plugged in). I checked 2 hrs later and the 12v battery was at 12.54v so the overnight charge of HV batteries did not seem to impact the 12v battery. Currently my charge level is 93% and if I was not concerned about the 12v battery I would probably wait at least another week before charging. I now have 220v wired up and my next charge will be with the portable charger at 12a.

More recently, I've been measuring the 12v battery (digital Fluke meter) immediately after arriving home (I also drive in L to take advantage of regen) and again immediately before I leave home (I'm retired so usually don't go out often or far). That method yields 12.9v arriving home and 22 hrs later 12.4v before starting out. So that is about a 0.5v parasitic drain.

The lowest voltage I have measured is 12.37v. Maybe this is normal, I dunno but don't want to find out the hard way. Since I am driving very low mileage every day I fall outside the normal operational situation.

My question is should I be plugging in and remaining plugged in (because I'm a low mileage driver) for the time the car is sitting in the garage in order to make sure the 12v battery is kept charged? I believe I read somewhere that a module periodically charges the 12v battery from the HV circuit but I don't know if the vehicle must be turned on for that to happen. Or maybe the range of 12.4-12.8 is normal and I should stop worrying about it unless/until it gets to 11.99v.

 

[GreyBolt]

I leave my Bolt plugged in L2 in the garage whenever I am not driving it (except for thunderstorm days). While new to the Bolt ('18, Premier), I had two VOLTs and left them plugged in too. At least by VOLT gen 2, the VOLT not only did some temperature regulation when needed, but it also took care of the 12V battery on its own using the internal APM. Automatic activities seemed to include 12V battery maintenance cycles, all sorts of odd curves and cycling when looking closely over time. I leave it plugged in more for what the car might do to adjust the HV battery temperature as needed, particularly for winter where temps at night can fall to -30F here in Dec/Jan). Also, I can start climate pre-conditioning at will, knowing it will run from the L2 power.

Unless I've missed something, most 12V battery problems are just from batteries wearing out or failing, or being left unattended for weeks, or months, not days.

The VOLTs had some awful failure modes, but most of those problems turned out to be bad 12V connections, I haven't seen anything like that here.

It is true that many VOLT / BOLT problems can be caused by a 12V battery problem, but not the converse, that there is any systematic Bolt 12V battery problem. Also, phantom power drain concerns seem to be more a Tesla issue, nothing significant with Volt or Bolt.

Trying to supplement the automatic charging and maintenance systems may do more harm than good in normal ops. If you need to leave it sit for months, that may be a different story. There was a thread about dealers needing to charge the 12V battery once in a while for long term sitting on a lot.

So, leave the 12V battery alone

But, if you drive low mileage most of the time, do check out the hill top function, no need to fully charge your HV battery each time, and some think the HV battery may last longer if not fully charge each time. Also, full regen is more available if not max charged at the beginning of the drive.

 

[jon8491]

So, leave the 12V battery alone

But, if you drive low mileage most of the time, do check out the hill top function, no need to fully charge your HV battery each time, and some think the HV battery may last longer if not fully charge each time. Also, full regen is more available if not max charged at the beginning of the drive.

OK, I sorta suspected this but wanted confirmation.
BTW, there is no longer a hill top function in the '19. There is a sliding scale and I've set it to 95% as a start (knowing that hilltop mode is lower than this). So my next charge will go to 95%. As it stands now, I'm at 93% so hardly worth the effort to do it at this moment.

If I'm racking up even as much as 10 miles a day and plugging it in ev day, 95% still will leave room for regen. If I do a 150+ mile marathon then I'll reduce that 95% slider to maybe 85% to leave room for those free electrons.
Thanks for the reply.

 

[drdiesel1]

Don't charge the car everyday if you're not driving it very far.
Let it drop down to at least 40% before doing another charge.

 

[Vertiformed]

Don't charge the car everyday if you're not driving it very far.
Let it drop down to at least 40% before doing another charge.

Also, be sure to climb in through the windows to save wear on the door hinges. Be sure to also avoid using your turn signals to avoid wear on the lamps. And, most importantly, try to drive another car in preference to the Bolt to avoid wear on the battery and drivetrain.

Alternatively, just drive the car and plug in every day like the car expects. There is no evidence at all that any Bolt has ever suffered any harm from plugging in every day, and no evidence that running it down to 40% and then recharging has any extra benefit for a Bolt.

For many of us, one of the great things about an EV is that you start the day with a “full tank” and pretty much never have to worry about being low on fuel in daily driving.

 

[drdiesel1]

Also, be sure to climb in through the windows to save wear on the door hinges. Be sure to also avoid using your turn signals to avoid wear on the lamps. And, most importantly, try to drive another car in preference to the Bolt to avoid wear on the battery and drivetrain.

Alternatively, just drive the car and plug in every day like the car expects. There is no evidence at all that any Bolt has ever suffered any harm from plugging in every day, and no evidence that running it down to 40% and then recharging has any extra benefit for a Bolt.

For many of us, one of the great things about an EV is that you start the day with a “full tank” and pretty much never have to worry about being low on fuel in daily driving.

Dude! Who said anything about harm or or benefit ????
Have you ever heard the term best practices ?

 

[Sean Nelson]

My concern is what may be a parasitic drain and if I don't charge often enough I will find a dead 12v battery.

That's a valid enough concern because the car is never truly 100% "off". It has a low-power "off" mode where it can still connect to or respond to queries over the internet (via its cellular modem), watch for approaching Bluetooth devices or key fobs, monitor battery temperatures and heat or cool the battery if necessary, etc. So yes, there's always some drain on the battery. And it's a relatively small battery because it doesn't have to supply the huge cranking current required to start an internal combustion engine.

But even when the car is off it's programmed to wake every so often and apply a charge to the 12V battery - so it's not normally a concern unless you're going to leave the car unused for more than a couple of weeks. In that case a trickle charger is a good idea, and you might also consider putting the vehicle into its low-power "Transport Mode"

Posters have reported exhausting the 12V battery by leaving the hazard flashers on for at least several hours, so that's also something to avoid. Note that when you turn the car "off" the "click-click-click" sound of the flashers is muted, which makes it easy to forget that they're on.

 

[ai4px]

I don't mean to be rude, but if you drive 2-4 miles a day, why do you have a car?

 

[GlenandhisBolt1!]

We can understand your affection for your new Bolt, jon8491. For me, it did taking some adjustment to owning a vehicle that requires so little attention.

Where do you live? The local climate can have a major impact on charging requirements.

The intent here is to maximize battery life: both the monster drive battery and fairly standard 12VDC battery. The drive battery must be maintained between 40 degrees F and 90 degrees F. If you live in a colder climate, the drive battery needs to be heated, and this is best accomplished by parking it in your garage and plugging it in. The vehicle may not be charging at all, simply applying power to the heating circuit on those cold winter days and nights.

You seem overly concerned about your 12VDC battery. Like GreyBolt said, just leave it alone. Failures seem to be rare. It will likely last about four years, regardless of what you do.

As far as 'best practices' for maximizing drive battery life:
The battery life of a rechargeable lithium ion battery is a function of (1) time, (2) temperature, (3) use, and (4) number of charge cycles.

(1) You can't do anything about Father Time, so let's leave that one alone.
(2) You are limited in what you can do about temperature, but if you live in hot or cold climate, keeping your Bolt in the garage may help your Bolt avoid extremes in temperature. You can do something about use. (3) Draining a rechargeable lithium ion battery is generally considered Not Good for it, as is charging it to full. The generally accepted practice is to keep it between about 15% and 85% of full charge. When it comes to use while driving, jackrabbit starts are probably undesirable, as this means higher discharge rates for the battery, which may not be the best for it.
(4) The number of charge cycles is a difficult subject if you live in a hot or cold climate, due to battery conditioning requirements. There may not be a way to set up the charging system so it only performs battery conditioning, and does not charge the drive battery. So if you live in a mild climate where battery conditioning isn't required, leaving the Bolt unplugged when it doesn't need charging may be a good plan, as this will reduce the number of charge cycles. The number or depth of charges to be expected from the drive battery is unknown, but the long warranty suggests that it's a big number: perhaps a thousand or more full charges.

Another factor may be use of DCFC charging. Engineers at Tesla have suggested that using high power ('Supercharger') charging on Teslas shortens battery life.

For the Bolt, the effectiveness of most of these 'best practices' are unproven, since it has only about two years of service life. It's possible that it is quite insensitive to charge/ discharge levels and frequency of charging. Drive battery life seems to still be an unknown, as owners with 50,000 miles are not yet reporting any meaningful loss of capacity.

 

[Vertiformed]

Dude! Who said anything about harm or or benefit ????
Have you ever heard the term best practices ?

Yes, I have. Generally best practices have benefits and/or avoid harm.

The whole point is that I would argue that the best practice for drivers is to begin each day with a car that has lots of miles it can drive, rather than a mostly-run-down battery. That way you're always ready for whatever life throws at you.

A good rule of thumb is that if you're the kind of driver who loved pouring additives into their gas tank or engine oil “to protect the engine, the most expensive part of the car”, you should totally adopt intricate charging strategies “to protect the battery, the most expensive part of the car”. Otherwise, just drive it, plug it in in whatever way what suits you most, and stop worrying.

 

[jon8491]

I don't mean to be rude, but if you drive 2-4 miles a day, why do you have a car?

I did consider just walking but the reality is I don't want to trek back and forth in sub-freezing temp's for 3-4 months of the year nor trek back & forth in triple digits for 2 months of the year.
And because I'm tired of trying to find a parking place in the ever-shrinking parking spaces designed for compact cars and not for my long-bed pickup. The Bolt seemed like a good alternative.
I naively figured I could plug it in once a week to charge it as needed.

 

[jon8491]

Don't charge the car everyday if you're not driving it very far.
Let it drop down to at least 40% before doing another charge.

That was my intention until I started noticing the fluctuations of the 12v battery and became concerned that perhaps my driving needs required a different charging routine. Maybe I should have waited a few more months to get a better handle on the 12v system before posting my query since opinions are all over the map.

 

[XJ12]

That was my intention until I started noticing the fluctuations of the 12v battery and became concerned that perhaps my driving needs required a different charging routine. Maybe I should have waited a few more months to get a better handle on the 12v system before posting my query since opinions are all over the map.

driving the car at least once a day should trigger a 12V battery charge if the voltage is below 12.56V.

https://www.chevybolt.org/forum/119778-post20.html

 

[drdiesel1]

That was my intention until I started noticing the fluctuations of the 12v battery and became concerned that perhaps my driving needs required a different charging routine. Maybe I should have waited a few more months to get a better handle on the 12v system before posting my query since opinions are all over the map.

You're over thinking this. Just charge it once a week and stop worrying about it.

12.6 volts is a full charged 12V battery. This car will take care of the 12V battery all by itself.

 

[drdiesel1]

Yes, I have. Generally best practices have benefits and/or avoid harm.

The whole point is that I would argue that the best practice for drivers is to begin each day with a car that has lots of miles it can drive, rather than a mostly-run-down battery. That way you're always ready for whatever life throws at you.

A good rule of thumb is that if you're the kind of driver who loved pouring additives into their gas tank or engine oil “to protect the engine, the most expensive part of the car”, you should totally adopt intricate charging strategies “to protect the battery, the most expensive part of the car”. Otherwise, just drive it, plug it in in whatever way what suits you most, and stop worrying.

Please take a hike. Thanks!

 

[jon8491]

driving the car at least once a day should trigger a 12V battery charge if the voltage is below 12.56V.

https://www.chevybolt.org/forum/119778-post20.html

Thank you for this comment and the link. Lots of valuable info there.

FWIW, twice in the past several days I have measured my voltage below 12.56v immediately prior to starting the vehicle.
Both times, checking approx 1.5 hrs later on return home the voltage was above 12.56.

I feel like I have a much better understanding.

 

[XJ12]

Thank you for this comment and the link. Lots of valuable info there.

FWIW, twice in the past several days I have measured my voltage below 12.56v immediately prior to starting the vehicle.
Both times, checking approx 1.5 hrs later on return home the voltage was above 12.56.

I feel like I have a much better understanding.

I've never checked my 12V battery voltage. I've had the car one year now and only charge once per week. Drive about 150 miles per week so I do run it longer. Don't have a 12V battery episode to report. All has been well.

 

[jon8491]

You're over thinking this.

No doubt, it's not the first time and probably won't be the last.

12.6 volts is a full charged 12V battery. This car will take care of the 12V battery all by itself.

As I originally posted, my concern arose out of various posts regarding the failure of this battery. When I checked the battery out of curiosity I found what I thought were large fluctuations, at least large based on my prior experience. The link to your well written 2017 post about Bolt 12v system helped me better understand.

Thanks for your help.

 

[drdiesel1]

No doubt, it's not the first time and probably won't be the last.



As I originally posted, my concern arose out of various posts regarding the failure of this battery. When I checked the battery out of curiosity I found what I thought were large fluctuations, at least large based on my prior experience. The link to your well written 2017 post about Bolt 12v system helped me better understand.

Thanks for your help.

You can't test the battery with the key on. The DC/DC charger is active.
It's the same thing when charging the HVB. 12V battery testing is done
without disturbing the system. Pop the hood and leave the car alone over
night. Open the hood without opening any doors. Leave your key in the house too.

Hook up your DVOM and check the 12V battery voltage. This is the true battery health data point.

 

[jon8491]

12V battery testing is done
without disturbing the system. Pop the hood and leave the car alone over
night. Open the hood without opening any doors. Leave your key in the house too.

A few days ago, after sitting 2 hrs, FOB far away it was 12.88v. Then next day, early morning (FOB far away) it was 12.8. Then prior to driving in late PM it was 12.37 with FOB in pocket.

I'll alter my procedure to check only when the fob is not nearby.
Thanks for this info.