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Lithium Ion [LiFepo4] Battery Charger for the 12V Battery

9K views 39 replies 11 participants last post by  Snorlax 
#1 · (Edited)
I will preface this post with the statement that I am no engineer, and my understanding of battery technology is amateurish at best. My experience with my GT so far has been great (with the exception of one day where the car briefly illuminated the red Drive system/High-voltage system/Vehicle electrical system; not repeated). Just the same, the posts here and here about the exhaustion of the 12V battery have made me want to have a backup plan. My GT is my DD, but there are times when she will be left unattended for a few weeks. The threads about the terrible delivery experience and the dead GT in the garage contain a couple of recommendations for 12V battery chargers, but none of the posters seem highly confident about their safe application to the GT.

The user manual for the GT is very clear on the specs for a charger to recharge the 12V battery at p. 242-3. The first spec is that charger must have a maximum charging voltage of 14.8 volts. The second spec is that the charger must specifically support LiFepo4 batteries with integrated protective electronics: The third spec is a maximum current of 90 amps. Here’s the excerpt:

Font Screenshot Rectangle Document Terrestrial plant


There are a variety of battery maintainers/rechargers that are suitable for the full range of lead-acid batteries, including AGM. Some chargers on Amazon claim LiFepo4 compatibility, but the number that actually seem spec’ed for LiFepo4 seems quite small. And many of those suffer from uneven or occasionally severely critical reviews. I found this one which, despite its almost kit-utilitarian appearance, enjoys good ratings and reviews from people who seem to know what they are doing, and it meets the Audi specs:
Font Cable Gadget Audio equipment Electronic device


Granted, at 6A of output, it’s not going to get you going in an emergency, but it seems to me it ought to work with zero risk of damage to the OEM 12V battery. There may be others even better suited. The price on this one is right.

Thoughts & recommendations?
 
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#4 ·
I will preface this post with the statement that am no engineer, and my understanding of battery technology is amateurish at best. My experience with my GT so far has been great (with the exception of one day where the car briefly illuminated the red Drive system/High-voltage system/Vehicle electrical system; not repeated). Just the same, the posts here and here about the exhaustion of the 12V battery have made me want to have a backup plan. My GT is my DD, but there are times when she will be left unattended for a few weeks. The threads about the terrible delivery experience and the dead GT in the garage contain a couple of recommendations for 12V battery chargers, but none of the posters seem highly confident about their safe application to the GT.

The user manual for the GT is very clear on the specs for a charger to recharge the 12V battery at p. 242-3. The first spec is that charger must have a maximum charging voltage of 14.8 volts. The second spec is that the charger must specifically support LiFepo4 batteries with integrated protective electronics: The third spec is a maximum current of 90 amps. Here’s the excerpt:

View attachment 3894

There are a variety of battery maintainers/rechargers that are suitable for the full range of lead-acid batteries, including AGM. Some chargers on Amazon claim LiFepo4 compatibility, but the number that actually seem spec’ed for LiFepo4 seems quite small. And many of those suffer from uneven or occasionally severely critical reviews. I found this one which, despite its almost kit-utilitarian appearance, enjoys good ratings and reviews from people who seem to know what they are doing, and it meets the Audi specs:
View attachment 3895

Granted, at 6A of output, it’s not going to get you going in an emergency, but it seems to me it ought to work with zero risk of damage to the OEM 12V battery. There may be others even better suited. The price on this one is right.

Thoughts & recommendations?
Hi Spyder, I chose the Noco Genius 10 because the leads had M10 terminal rings that fit on threaded portion under the GT charging posts and the leads are detachable so I could leave them in place permanently in case frunk would not open and I needed to charge from outside the frunk. The Noco, according to manual, in Lithium mode does 14.6V, 10 amps. Noco Genius 10 at US$100 is also more money than the one you found. I am not an electrical genius so buyer beware :)
 
#5 ·
#16 ·
The manual provides that ‘the high-voltage battery supplies the 12 volt battery’ (pg 242) So if you keep the main car battery charged via the car charger while the car is not used for an extended period of time, why would you need to separately maintain the 12 volt battery?
 
#19 ·
No offense intended, but if you’ve read the full thread, I would think you would see how this happens. The point is to have a solution if and when it does. I charge my car more than once a week, but one never knows what the future might bring. And many people don’t have constant access to a charger.
 
#18 ·
Because it seems to mostly charge the 12v battery while driving. if you leave it for extended periods of time without driving and there is some drain on the 12v, it won't get recharged, it seems. I've read elsewhere that running the HVAC will cause the 12v to get recharged even if not driving. I have been unable to confirm this is how it actually works, but it makes sense that the HVAC is powered by the HV battery and not the 12v.
 
#26 ·
Some of you here with previous EV experience may be aware of similar challenges with other cars. I’m not sure it makes me feel better that we’re not alone in these difficulties. In fact, to me it’s even more frustrating that Audi would implement such a craptacularly boneheaded frunk access mechanism when 12V battery failure is a known issue in the industry. This video by an Ioniq 5 owner illustrates the Hyundai “solution”: a mechanical frunk release! According to this fellow, there appears to be a rather widespread problem with the 12V battery “weak link” in a lot of EVs. Of course it’s worse with lead-acid batteries as opposed to LI, but as this forum shows, LI batteries can be exhausted as well.

My car is about to enter week three at the PPF shop. So far, it has held its SOC like a champ. There’s been no battery drain whatsoever, at least according to the app. Still, with probably another week to go, mostly to finish the rims and calipers, I’ll be keeping my fingers crossed. And I’ve told the shop not to lock the hood shut, though I have no idea if leaving the hood open causes any sort of current draw. As part of my custom radar detector installation, my installer is going to run leads to an easily accessible and weather-safe location.
 
#28 ·
I will preface this post with the statement that I am no engineer, and my understanding of battery technology is amateurish at best. My experience with my GT so far has been great (with the exception of one day where the car briefly illuminated the red Drive system/High-voltage system/Vehicle electrical system; not repeated). Just the same, the posts here and here about the exhaustion of the 12V battery have made me want to have a backup plan. My GT is my DD, but there are times when she will be left unattended for a few weeks. The threads about the terrible delivery experience and the dead GT in the garage contain a couple of recommendations for 12V battery chargers, but none of the posters seem highly confident about their safe application to the GT.

The user manual for the GT is very clear on the specs for a charger to recharge the 12V battery at p. 242-3. The first spec is that charger must have a maximum charging voltage of 14.8 volts. The second spec is that the charger must specifically support LiFepo4 batteries with integrated protective electronics: The third spec is a maximum current of 90 amps. Here’s the excerpt:

View attachment 3894

There are a variety of battery maintainers/rechargers that are suitable for the full range of lead-acid batteries, including AGM. Some chargers on Amazon claim LiFepo4 compatibility, but the number that actually seem spec’ed for LiFepo4 seems quite small. And many of those suffer from uneven or occasionally severely critical reviews. I found this one which, despite its almost kit-utilitarian appearance, enjoys good ratings and reviews from people who seem to know what they are doing, and it meets the Audi specs:
View attachment 3895

Granted, at 6A of output, it’s not going to get you going in an emergency, but it seems to me it ought to work with zero risk of damage to the OEM 12V battery. There may be others even better suited. The price on this one is right.

Thoughts & recommendations?


I went with this charger which so far has worked great.

Mroinge 12V 2A Lead Acid & Lithium(LiFePO4) Automatic Trickle Battery Charger Smart Battery Maintainer for Car Motorcycle Lawn Mower Boat ATV SLA AGM Gel Cell Lithium(LiFePO4) and More Batteries
by Mroinge
Learn more: https://www.amazon.com/dp/B07MCTXFC7/ref=cm_sw_em_r_mt_dp_AQ7FQ1Y4HWGT9AM5QHCB?_encoding=UTF8&psc=1
 
#30 ·
Not that I could see in the app. Every time I look at the Hyundai Bluelink app (my daughter has a Kona), I am envious. Though in that video I posted above, the app reported his 12V battery as good, even though it was dead.
 
#36 ·
I use NOCO En Genius chargers for all my cars and I have already sent the dealer up an adapter to install in my car when it arrives. If I had not read about what can happen on this forum, I would not have thought it would be needed on an EV (this will be my first, so I am learning from all of you), I also have extra batteries for some of my car and a battery charger (big one on wheels like shops use) and conditioner. I have winter and summer cars and my summer cars go into storage on Nov 1st and then come out on April 1st and with the exception of my dog's transport jeep the winter cars go into storage on April 1st. The E-Tron will replace the s class coupe as an all-year car. I have seen first hand (someone I know was too impatient to wait a couple hours for me to come over help him so he friend his Ferrari's electronics trying to jump it) what jumping a car not meant to be jumped can do. I also keep my keys in Faraday boxes so the cannot communicate with the car.
 
#37 ·
It’s been a while for this topic, but I thought I would share what I did to make sure I never had this problem—and of course, by doing so, ensuring that it never happened in the first place. ;)

I’ve had a Stinger radar/laser defense system installed in the GT, along with a FitcamX, and a few other conveniences. Today was testing day to make sure everything works properly before I retrieve her tomorrow. I asked my shop to install one of those 12V ports you see on RVs. We looked at putting it in the glovebox, but he recommended (and I agreed) placing it to the left of the driver under the side panel, along with the USB port for interacting with the Stinger. Here are a couple of pics.
Automotive tire Automotive lighting Hood Vehicle Trunk
Automotive lighting Automotive tire Motor vehicle Automotive design Automotive exterior
 
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#38 ·
How do you like the FitcamX?

I like the look of it and hardwired a front and rear dashcam in my RS3 last year. Would make a good little project.

Also, out of curiousity, what made you go with Stinger over ALP? It seems like ALP has had the best reviews for years (but the Stinger is a lot more discrete)
 
#40 ·
That is incredibly helpful information, thank you for all of that. Makes me want to find a Stinger dealer near me. If you don't mind, how much did that whole thing run you? Feel free to PM me as well

I live in CT and laser is everywhere. I often drive home late at night with nobody on the road (2-3 AM) except for the troopers :)
 
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