Charging the 12V battery if car is not driven much

[cove3]

After replacing my BMW 528E and 525I 12V batteries every few years, I was told by BMW to use a trickle charger to the cigar lighter if a car is not driven much, which was the case my being retired. The battery life is reduced if they are undercharged from lack of driving. The batteries draw some current constantly even if the car isn't used, and I found myself charging them from dead with a charger..

I'm wondering about the e-golf battery when the car isn't driven much. With the snow I haven't used it for over a month:
1. The manual says the battery will drain if not driven for long periods, the doors are unlocked, or lights left on
2. It appears the 12V battery is charged from an alternator while driving
3. The battery capacity is small as it's not needed for starting like an ice, so the safety margin is less
4. The manual says only the dealer should charge it and that the dealer has to reset things when changing a battery
5. There doesn't seem to be an indicator for the 12V battery state of charge

This leaves 3 questions:
1. Is it really necessary for the dealer to charge the battery.
2. How to tell if it's in the danger zone of discharge?
3. Is it safe to use a trickle charger through the cigar lighter as with my ICE to to be on the safe side?

Ron

 

[tigger19687]

There must be something wrong if you are going through 12v batteries like candy !?

If you are going to leave a car unused for more then or about a month I would disconnect it.

My trucks don't go through batteries unless I leave a light on or don't drive it for 4 months straight.

Not sure if you have Electronics in the car (navigator etc) that are not turned off ?
Or, like my son, who leaves things plugged in the lighter of the truck.

 

[cove3]

Not like candy, but every 2 years or so. Disconnecting the battery isn't practical, as I use the cars for the grocery and short trips, but these trips aren't enough to charge the battery up. I was periodically finding them dead and charging them in the garage. So BMW told me the battery life was shortened by being at a low state of charge over time. That's the reason trickle chargers are sold.....to keep the battery topped up.

The question is, is there any way to tell the state of the 12V battery, and can/should you use a trickle charger with an electric car or is there some circuitry which would advise against it.

I know the battery is draining. Responding to car net, a red light flashes every few seconds to show the car door is locked, etc.

Ron

 

[rjnerd]

First, the e-golf has much lower demands on its "house" battery. No starter to turn, so it doesn't take much to get to "ready", just enough to pull in the contactors in the HV pack. It is the case that all modern cars have more idle drain than in years past, if nothing else, powering the various receivers for the key fob, and the car-net system. (in the old days, key off meant the only thing drawing power was the clock)

The house battery is charged by a dc->dc converter from the hv pack, no alternator to worry about. It should be fine with a battery tender, but not thru the lighter socket, as those are usually disconnected when the car is. You can get a tender with a quick disconnect cable long enough to reach thru the grille slot, making it easier to reach.

Your short trips should be sufficient to keep it topped up. especially since the converter is a more intelligent charging system than your old alternator, and isn't dependent on engine speed to get peak charging output. Your old car at idle may or may not have had enough output to cover the load of ignition and fuel injection, back in the day when cars had ammeters rather than check engine lights, it would take a bit of revving to get the thing to the positive side. As soon as the contactor clicks in, the house battery will be charged to full as soon as is reasonable.

One thing to consider, if the battery does lose it, make sure its replacement is "deep cycle" rated. (simple way to tell, it will be a lot heavier than the one it replaced). It will be much more tolerant of sitting around.

 

[cove3]

Thanks rj. Very helpful

1. While it's true there's no start load as with an ICE, this also allowed VW to use a small battery so concerns still exist
2. There's nothing in the manual as to how long the car can be sitting idle before the 12V battery drains below a safe thresh hold. 3 weeks, 2 months?
3. Nor is there any easy way to test the capacity or state of charge to know whether to use a trickle charger.
4. Does the 12V battery get charged when you charge the main battery? If so, and the main battery is at 50% for storage puroses, I could charge it to 80% in order to top up the 12V battery
5. It appears the 12V socket requires the ignition to be on, but in any event the manual says not to put a charger, solar or any power input into the socket
6. Looking in the engine compartment, there don't seem to be any openings in the grill to run a trickle charger through, so the hood would have to be up
7. If the 12V battery is charged by the car main battery, couldn't I just turn on the electric motor for a couple of hours?
8. I called my dealer service and they said the 12V system is just like an ICE and is independent of the main battery system, and I could charge it with either a trickle charger or battery charger without loosening any battery connections

Ron

 

[NeilBlanchard]

The 12V battery is charged with a DC-to-DC converter, so it should last as long as any regular battery.

In my experience, 12V lead acid batteries last at least 5 years, and as long as 7 years. If it only lasts 2 years, then there is something else going on.

 

[cove3]

<<<12V lead acid batteries last at least 5 years, and as long as 7 years. If it only lasts 2 years, then there is something else going on.>>

That's probably right if kept in a reasonable state of charge, but since retirement I was using my cars so little that the batteries were not charged up much, and coupled with normal constant drain, meant the batteries were sitting in a low state of charge for months on end. BMW service told me that's why the batteries were failing after 2 years, and that I should keep them on a trickle charger to extend their life.

The main egolf battery is the same per them manual. It should not be allowed to go below 10% or so for an extended preriod or you will shorten the capacity and life

Ron

 

[cove3]

The e-golf service rep said the 12V battery is charged by an alternator and not by the traction battery, either during charging or while driving the car. The owners manual also references an alternator on Page 15 and 301

He said to use a trickle charger if the car is not driven for several months, but not through the 12V convenience outlet. This doesn't work anyway if the motor isn't activated and if it is, the manual says not to put any kind of power like a trickle charger or solar into the 12V outlet.

Ron

 

[NeilBlanchard]

What alternator would that be?

Hint: there is no alternator in the e-Golf.

It has to be a DC-to-DC converter, powered by the main high voltage battery pack.

 

[cove3]

See page 15 and 300 of the owners manual. There are 2 possibilities:

1. The manual is wrong. This is possible as the manual does have some references which can only apply to an ICE car
2. The service rep is wrong, although I thought I was talking to the man who went to e-golf school

If it is charged from the traction battery, it would seem the 12V should be charged while charging the traction battery or when the electric motor is activated, but the rep said the 12V is only charged by driving the car

Ron

 

[NeilBlanchard]

IF there is an alternator, it would be physically driven by the electric motor. Have you looked under the hood, and/or looked at technical images of the e-Golf drivetrain?

When / if you find the alternator, please inform us.

Do you see a power takeoff on the e-Golf motor that would spin an alternator?

 

[GadgetGav]

From a Green Car Congress report written after a visit to the Wolfsburg plant ahead of the US launch:

"The power electronics module controls the high-voltage energy flow between the e-motor and the lithium-ion battery (between 250 and 430 V depending on the battery voltage). The power electronics converts the direct current (DC) stored in the battery to alternating current (AC). The primary interfaces of the power electronics are its traction network connection to the battery; 3-phase connection to the electric motor; connector from the DC/DC converter to the 12-V electrical system; and a connection for the high-voltage power distributor."

Source: http://www.greencarcongress.com/2014/07/20140721-egolf.html

From that it seems that the 12V system is charge from a DC-DC converter from the main battery pack, but it's still not clear if the power electronics module is awake enough to trigger that DC-DC conversion if the car isn't in use. Maybe the 12V system could run down if the car is 'off' because the main power electronics module may only come on when you press that 'Engine Start' button...

 

[Kosta]

After replacing my BMW 528E and 525I 12V batteries every few years, I was told by BMW to use a trickle charger to the cigar lighter if a car is not driven much, which was the case my being retired. The battery life is reduced if they are undercharged from lack of driving. The batteries draw some current constantly even if the car isn't used, and I found myself charging them from dead with a charger..

I'm wondering about the e-golf battery when the car isn't driven much. With the snow I haven't used it for over a month:
1. The manual says the battery will drain if not driven for long periods, the doors are unlocked, or lights left on
2. It appears the 12V battery is charged from an alternator while driving
3. The battery capacity is small as it's not needed for starting like an ice, so the safety margin is less
4. The manual says only the dealer should charge it and that the dealer has to reset things when changing a battery
5. There doesn't seem to be an indicator for the 12V battery state of charge

This leaves 3 questions:
1. Is it really necessary for the dealer to charge the battery.
2. How to tell if it's in the danger zone of discharge?
3. Is it safe to use a trickle charger through the cigar lighter as with my ICE to to be on the safe side?

Ron

I would say the easy fix is to take it for a drive once a week for giggles , you have time , the vehicle depreciates regardless if you use it or not , and no special actions are needed then to quell your worry on a 12 v battery

 

[RonDawg]

While it's true there's no start load as with an ICE, this also allowed VW to use a small battery so concerns still exist

Comparing the batteries of my eGolf and my gasoline-powered Alltrack, the eGolf's battery isn't a whole lot smaller. It appears to use the same battery tray as the ICEV versions so when the eGolf's battery dies you can put in a standard size replacement; there's even a third bolt hole for it. It's also bigger than the battery I remember from my Leaf, which is quite small, but appeared to be the same size as the battery on my 1982 Honda Accord.

There's nothing in the manual as to how long the car can be sitting idle before the 12V battery drains below a safe thresh hold. 3 weeks, 2 months?

I've left my car at an offsite airport parking structure for 3 weeks, and had no problem turning on the car upon my return.

Nor is there any easy way to test the capacity or state of charge to know whether to use a trickle charger.

If it makes you feel better, use the trickle charger. If it's a true trickle charger and it is working properly, it won't overcharge your battery.

Does the 12V battery get charged when you charge the main battery? If so, and the main battery is at 50% for storage puroses, I could charge it to 80% in order to top up the 12V battery

Not sure on the eGolf, but that was NOT the case on the Leaf. In fact, leaving a Leaf plugged in for far too long actually drains the 12 volt battery.

Looking in the engine compartment, there don't seem to be any openings in the grill to run a trickle charger through, so the hood would have to be up

On my Alltrack (which I rarely use) I just leave the hood down but not fully shut; it's the same state if you pull on the inside hood release lever but don't open the hood. That also serves as a reminder that I need to unplug the trickle charger.

If the 12V battery is charged by the car main battery, couldn't I just turn on the electric motor for a couple of hours?

You could, but I would think it's easier to attach a trickle charger if it will not be used for some time.

I called my dealer service and they said the 12V system is just like an ICE and is independent of the main battery system, and I could charge it with either a trickle charger or battery charger without loosening any battery connections

Again if it makes you feel better, use the trickle charger.

EDIT: I just realized I'm replying to a 2+ year old thread but I'll leave my answers up anyway should someone's search take them here.

 

[miimura]

Thanks for you nice post. To charge battery with DC 12v to AC 110v 400w power inverter is easy to me. Since I have used this car charger for a long time. Simply to connect it with car cigarette lighter charger outlet. The advantage that I know about this tool is soft and convenient to take away. If you want to catch more information about it, you can click here to get. Best regards.

Please stop spamming us with your Bestekmall links.

 

[Mena]

There must be something wrong if you are going through 12v batteries like candy !?

If you are going to leave a car unused for more then or about a month I would disconnect it.

My trucks don't go through batteries unless I leave a light on or don't drive it for 4 months straight.

Not sure if you have Electronics in the car (navigator etc) that are not turned off ?
Or, like my son, who leaves things plugged in the lighter of the truck.

Yes, you're right. Car batteries can be drained if you leave electronics on when the car is parked or even when the car is unused for months. I often forget unplugging out my bestek 300w power inverter and just think that it doesn't matter if my phones or other connected things are plug out. While, after I do that for a long time, just found that I can't jump my car on the road. So, finally, I used a jump starter. The 4S store told me my car battery was damaged. But not so bad. So I have to remember to turn off the head lights and all my devices charged in car.

 

[Nick]

The 12v battery on my 2016 SEL is an AGM (applied glass mat). It has very low internal resistance and will not self-discharge substantially over several months. My car was in the garage for 7 weeks this summer, and started up normally when I got home.

 

[JoulesThief]

The 12v battery on my 2016 SEL is an AGM (applied glass mat). It has very low internal resistance and will not self-discharge substantially over several months. My car was in the garage for 7 weeks this summer, and started up normally when I got home.

AGM is Absorbent Glass Mat. The Fiber Glass Mat absorbs the sulfuric acid in between the lead plates.

http://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

 

[BomBoi]

Bumping up for a positive answer to see if i can trickle charge the 12v battery through the cigarette lighter.


EDIT: i will just try it and report back .

 

[flyboy320]

Bumping up for a positive answer to see if i can trickle charge the 12v battery through the cigarette lighter.


EDIT: i will just try it and report back .

Did it work?