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Does main battery keep 12v battery charged, when car is off?
I have some lights linked directly to 12v battery, so if i leave them on, will the main battery keep the 12v battery charged, even when car is off?


-LaBrother
 

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p. 154 in the manual

Battery Power Protection
The battery saver feature is designed to protect the vehicle's 12-volt battery. If some interior lamps and/or the headlamps are left on and the vehicle is turned off, the battery rundown protection system automatically turns the lamp off after some time.

p. 247 in the manual

Add-on equipment can drain the vehicle's 12-volt battery, even if the vehicle is not operating. When adding electrical equipment, it should only be connected using the accessory power outlets. The maximum power that can be supplied by one accessory power outlet or spread across all three is 200watts or 15amps. Exceeding 200watts or 15amps may cause erratic vehicle operation.
 

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The 12v battery is charged/maintained whenever the traction battery is charged. When the traction battery is not being charged, it is physically disconnected from the other circuits in the car, which is to say it has no means to charge the 12v battery.

I wonder if the traction battery also connects when the car runs the battery heater to maintain sufficient temperature in cold climates? In this case it should also charge the 12v battery.
 

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from this thread:

http://www.chevybolt.org/forum/230362-post33.html

When the vehicle cord is plugged in
The Hybrid/EV Powertrain control module (HPCM2) will check the 12V battery every 6 hours if the ignition is off. If the voltage is below a temperature dependent threshold ranging from 12.1 (cold) to 12.4 (warm)V, the Hybrid/EV Powertrain control module (HPCM2) will send the voltage set point to the engine control module (ECM). The engine control module (ECM) will send this to the 14V Power Module. Battery maintenance mode will charge the battery for 2-3 hours. If the Ignition is ON, the APM will cycle on as needed to maintain the 12V SOC.

When the vehicle cord is not plugged in
The Hybrid/EV Powertrain control module (HPCM2) will check the 12V battery every 4 days (2.5 to 3 days) and if the voltage is below a threshold of 12.0 may activate battery maintenance. If the high voltage battery state of charge is greater than 40% and the propulsion system is not active, Hybrid/EV Powertrain control module (HPCM2) will send the voltage set point to the engine control module (ECM). The engine control module (ECM) will send this to the 14V Power Module. Battery maintenance mode will charge the battery for 45-90 minutes..
 

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trickle charging the 12 volt battery

For the first time, I kept my 12 volt battery trickle charged with the system in service mode, during a power outage that killed my internet connection. I still had power due to my use of a propane generator. I used the wireless network in the car to power all my house wireless network. I found that my 5 amp trickle charger could not keep up with the power drain from the 12 volt battery, so next time, I am going to try my 10 amp trickle charger. I was a bit cautious and did not use the wireless network more than 3 hours. I know from experience that without trickle charging, the 12 volt battery goes completely dead after 5 hours in service mode.
 

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I have read some threads espousing, and then adopting into my own practice, periodic trickle charging. The argument is that using the 12-V to "open the door" to the HV batteries (plus using other utilities) does NOT "shake the crud off the plates" like the cold-cranking amps needed to engage a starter motor. I trickle charge once a month (overnight). Every time I connect it, it shows that it is "charging" (blinking light; presumably because it is less than "full") and, hours later, that it is "done" (solid light; presumably because it is "fully charged"). Maybe it was a waste of $13.99, but I tell myself I am keeping the 12-V in optimal shape for a longer-that-usual lifespan.
 

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I know from experience that without trickle charging, the 12 volt battery goes completely dead after 5 hours in service mode.
Recognise that from my other car. I did a lot of OBDII analysis on my Outlander PHEV (two apps have been created based on my research). For this, I needed CANBUS and most of the ECUs active for sustained periods of time. Putting the car in ACC mode (or service mode as you call it) would drain the battery in a few hours. To prevent this, I would keep the car ON. Every now and then, somebody would ring my door bell telling me I forgot to turn off my lights and my aux battery was draining. When I tried to explain to them I was running my lights in order to charge my aux battery, mostly they would think I was crazy. Quite understandably :D
 

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For those who are not electrical engineers, are we saying that an ICE car, using the alternator, tries to keep the 12-volt fully charged at all times (probably because it has to crank the engine in cold weather)? But that the Bolt doesn't? And that's ok?
 

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For those who are not electrical engineers, are we saying that an ICE car, using the alternator, tries to keep the 12-volt fully charged at all times (probably because it has to crank the engine in cold weather)? But that the Bolt doesn't? And that's ok?
Both EVs and ICE attempt to keep 12v battery fully charged. Alternators always run when an engine is running, and it supplies whatever power requirements are placed on the vehicle (radio, wipers, lights, computer, etc). It also charges the battery if it falls below some threshold. It varies the output based on the electrical needs. In the same way, EVs charge the 12v battery any time the car is "on". The 12v battery is also charged periodically based on the thresholds mentioned by XJ12.

The 12v battery should not be discharged more than necessary, as the longevity of the battery depends on depth of discharge and duration.

In other words, lead-acid batteries like to be fully charged at all times, and lithium-ion batteries like to remain around half charged.

Trickle charging likely has little benefit since it essentially gets trickle charged while the car is plugged in if it drops below some threshold.
 

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Trickle charging likely has little benefit since it essentially gets trickle charged while the car is plugged in if it drops below some threshold.
It is my understanding that the auxiliary (12V) battery is charged when the main HV battery is *charging*, but not when the vehicle simply plugged into the wall. Also, the 12V battery is maintained while the car is in "run" mode as well as there being a verification of the voltage in the aux battery every X days (?72 hours?) if the car hasn't been turned on. IMO, the voltage level is rather low at which charging is initiated in the latter case.

Trickle charging is a good idea- it gives your 12V battery a good saturation charge every few weeks. When I trickle charge EV aux batteries, I never see a battery show 'full' in less than 5 hours (unless I had previously charged it to full, unplugged the charger, and then re-started a 'charge' the next morning after no use). Now, the battery wasn't *seriously* depleted (that would have taken over 18-24 hours with my maintenance trickle charger) but the aux battery is almost never *full* in an EV: the drain due to car electronics has gone up considerably over the past 5-8 years or so.
 
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It is my understanding that the auxiliary (12V) battery is charged when the main HV battery is *charging*, but not when the vehicle simply plugged into the wall. Also, the 12V battery is maintained while the car is in "run" mode as well as there being a verification of the voltage in the aux battery every X days (?72 hours?) if the car hasn't been turned on. IMO, the voltage level is rather low at which charging is initiated in the latter case.

Trickle charging is a good idea- it gives your 12V battery a good saturation charge every few weeks. When I trickle charge EV aux batteries, I never see a battery show 'full' in less than 5 hours (unless I had previously charged it to full, unplugged the charger, and then re-started a 'charge' the next morning after no use). Now, the battery wasn't *seriously* depleted (that would have taken over 18-24 hours with my maintenance trickle charger) but the aux battery is almost never *full* in an EV: the drain due to car electronics has gone up considerably over the past 5-8 years or so.
I think we share the same understanding of how it works. My comments on charing behavior are based on the correction XJ12 gave. Of course trickle charging will help to extend the useful life, but if the other days of the week it isn't getting topped up, then the benefit is likely less significant. I'd probably only bother with trickle charging if I planned to let the vehicle sit for several weeks.

The real killer of most batteries is that one time a door is left ajar and the lights stay on. Any deep discharge is going to cause permanent wear and possibly kill the battery.

If I owned a Bolt, I would consider running the battery leads into the cabin and connecting a 20 Ah LiFePO4. They don't tolerate charging below freezing temperatures, so that's why I would move it inside. I would expect the LiFePO4 to last the life of the traction battery as long as it was never run flat accidentally. I'm 3 years in on a LiFePO4 in my Prius.

As extra insurance against a dead battery, you could carry a jumper battery.

This one is on sale for $39 using code TK7FGUVV

http://www.amazon.com/GOOLOO-15000mAh-Starter-Portable-Battery/dp/B01N3142JE
 

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It is my understanding that the auxiliary (12V) battery is charged when the main HV battery is *charging*, but not when the vehicle simply plugged into the wall. Also, the 12V battery is maintained while the car is in "run" mode as well as there being a verification of the voltage in the aux battery every X days (?72 hours?) if the car hasn't been turned on. IMO, the voltage level is rather low at which charging is initiated in the latter case.

Trickle charging is a good idea- it gives your 12V battery a good saturation charge every few weeks. When I trickle charge EV aux batteries, I never see a battery show 'full' in less than 5 hours (unless I had previously charged it to full, unplugged the charger, and then re-started a 'charge' the next morning after no use). Now, the battery wasn't *seriously* depleted (that would have taken over 18-24 hours with my maintenance trickle charger) but the aux battery is almost never *full* in an EV: the drain due to car electronics has gone up considerably over the past 5-8 years or so.
Again, recognise this from the Outlander PHEV: 12 volt is provided by the drive battery via a DC/DC converter when the car is in use or being charged. Apart from that, every day at 02:00 pm the aux battery receives a top up. But only in higher spec'd models models that have a WiFi access point.

When the car is hooked up but not charging, the BMU is asleep and the drive battery is disconnected from the vehicle. 12 volt is coming strictly from the aux battery.
 

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Tonight we have scheduled power outage from 10 PM to 6 AM Sunday. I bought Xantrex PROWatt 2000 Inverter got the 12v cables and about to connect hook it to the Bolt. Plan to have the 8 amp refrig running all night. . . Question to all those who have experienced the removal of the 12v battery from the Bolt, what happens when you reconnected it? What settings if any arel be lost? I suspect that the Bolt will be temporarily disconnected from 12v power and wonder ahead the effect. Thanks in advance for comments.
 

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Tonight we have scheduled power outage from 10 PM to 6 AM Sunday. I bought Xantrex PROWatt 2000 Inverter got the 12v cables and about to connect hook it to the Bolt. Plan to have the 8 amp refrig running all night. . . Question to all those who have experienced the removal of the 12v battery from the Bolt, what happens when you reconnected it? What settings if any arel be lost? I suspect that the Bolt will be temporarily disconnected from 12v power and wonder ahead the effect. Thanks in advance for comments.
If I recall correctly, temporary disconnect of 12v only caused the vehicle to forget home location, it remembered the radio stations and other preferences and settings.
good luck...
 

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Various theories of helping or hurting the 12-volt system and the main propulsion system are regular fodder here and we've got some very intelligent and experienced professionals thinking about it and discussing it.

FWIW, a Bolt engineer I know from a former life looks in on this forum from time to time, but is forbidden by corporate policy from commenting. His answer to this and other similar battery questions, "We've done everything cost-effectively possible with current technology and software to make the system idiot-proof. There's nothing necessary to help make the battery live longer and it's very difficult for normal owner-driver operation to shorten battery life."

I did quote to him, "The difference between genius and stupidity is genius has it's limits." He admitted someone, somewhere, might find a way to kill a battery, "But it will be curious idiot with a screwdriver trying to hack into one of the systems; nothing to do with normal driver operation."

Bottom line - 12-volt batteries are normal wear parts and will have to be replaced occasionally. The Bolt 12-volt management system is far superior to those on ICE which have high starting drain when cold and then must be recharged by an alternator.

A bit off topic, but interesting bit of battery lore. BMW ICEs came programmed with the alternator to only charge when the throttle pedal was off and the car in coasting mode. That worked in Europe, but not for US urban stop-and-go traffic; batteries were not being kept charged. Their first solution they thought of was to change the charging software to be voltage regulated. However, the reason for the original software was another one-tenth of a MPG savings on the EPA cycle. No changes allowed which would affect that posted MPG. The solution implemented was to replace the battery annually when the car was in for oil changes. The owners really loved that when warranty and the free oil changes expired.

jack vines
 

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He admitted someone, somewhere, might find a way to kill a battery, "But it will be curious idiot with a screwdriver trying to hack into one of the systems; nothing to do with normal driver operation."
I think the biggest risk to the 12V battery is for the car to be left idle and disconnected for several months. I suspect that people buying Bolts that sat around untended on dealer lots for too long accounts for a lot of the 12V battery issues we hear about.
 

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"We've done everything cost-effectively possible with current technology and software to make the system idiot-proof. There's nothing necessary to help make the battery live longer and it's very difficult for normal owner-driver operation to shorten battery life." Ok, nicely phrased soothing and comforting statement. The question deep in my core remains "Is it better to charge from day 35% to 85% in one shot or is it better to charge 10% here, and 15% there when you can?. I suspect the answer could be something like one method of charging does have a more strenuous effect on the batter than the other, but the difference is negligible that one battery concern should be focus elsewhere. As a more experienced member said I sounds correct, there just (yet) isn't enough data to say conclusively.

Now to the point at hand. Yes the power went out last night as scheduled by SCE and returned this am around 6. Here's what happened with the Bolt. To connect the Xantex inverter to the battery I decided to remove the two square bolts (one at each battery terminal) and replaced them with longer ones so that I can just screw on the inverter cable and remove it without having to remove the battery cable from the vehicle. Connected the inverter turned it on and put a small load on it (about 2 amps). Everything worked as expected but within a few minutes the battery voltage started to drop from 13.0 quickly down to 12.2 when I removed the inverter load and started the vehicle (Bolt). The voltage at the battery jumped to 13.4 and then 13.9. I restarted the load and the battery voltage dropped to 12.9 and remain there.

From this I concluded that there's no charging of the 12v battery with the car off. (Someone mentioned that it checks it in 6 hour increments), but it does seem to charge it immediately after turning the vehicle on. I didn't record the percentage of propulsion battery before and after, I should have. Heres's a couple of pics . . . I've learned a great deal in this forum and trying to give back a little ;)
 

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From this I concluded that there's no charging of the 12v battery with the car off. (Someone mentioned that it checks it in 6 hour increments), but it does seem to charge it immediately after turning the vehicle on. I didn't record the percentage of propulsion battery before and after, I should have. Heres's a couple of pics . . . I've learned a great deal in this forum and trying to give back a little ;)
The car is designed so that all 12 volt battery loads turn off within ten minutes of turning off the car. With no loads, the battery is fine sitting for 6 hours, at which point the car will check the battery, and charge if needed. If you go around the designed system, and hook a load to the battery, with the car turned off, it won't know until it checks in six hours, by which time you could have drained the battery dead, taking out the car's computer, so the car can't check back.

The Bolt's accessory battery is 50 Ah capacity. Lead acid batteries should not be discharged below 50%, so you have ~12 volts x 25 Ah = 300 Wh of usable power from the battery before it requires recharging.

If you are going to run anything off the car's battery for more than a few minutes, you will need it turned on, so the DC-DC inverter can maintain full voltage. If you leave it turned on, in Park, it will turn itself off in two hours, if I remember correctly. Apparently, you can get around this by starting it from the passengers seat, with one hand on the brake pedal, then put on the parking brake, and shift into Neutral. Leave the fob in the car, leave by the passenger door, and the car should stay on. I suggest turning off the driving lights, dimming the dash lights, turn the radio all the way down, turn off the climate system, and depress the volume knob until the center screen asks you if you want it to go black. Whew!
 

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A bit off topic, but interesting bit of battery lore. BMW ICEs came programmed with the alternator to only charge when the throttle pedal was off and the car in coasting mode. That worked in Europe, but not for US urban stop-and-go traffic; batteries were not being kept charged. Their first solution they thought of was to change the charging software to be voltage regulated. However, the reason for the original software was another one-tenth of a MPG savings on the EPA cycle. No changes allowed which would affect that posted MPG. The solution implemented was to replace the battery annually when the car was in for oil changes. The owners really loved that when warranty and the free oil changes expired.

jack vines
That is a great side story! Thanks for sharing it...
 
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