# The 12 Volt battery in the Model 3, not AGM?



## Long Ranger

I frequently see statements that the 12V lead acid battery in the Model 3 is an AGM battery, but I don't believe this is true. I can't find anything authoritative that states it's an AGM battery. I often see this website quoted as a source:
https://teslatap.com/articles/12-volt-battery-compendium/ but they don't really provide any evidence for their claim that the AtlasBX 85B24LS uses AGM technology.

However, if I go to the battery manufacturer's website, it's pretty clear to me that this is not an AGM battery. Hankook doesn't quote very complete specs, but here is the evidence that I can see:
1. Per https://cdn.hankook-atlasbx.com/PRD...3451a848e7e5/HANKOOK_AtlasBX_small(final).pdf the part number is MF85B24LS. All of their AGM batteries start with an AGM prefix. All of their Sealed Maintenance Free batteries start with this MF prefix.
2. The MF85B24LS https://www.teslarati.com/tesla-model-3-dashcam-power-12v/ looks exactly like the AtlasBX SMF JIS family of batteries (except for the handle color) https://www.hankook-atlasbx.com/en/product/automotive/passenger-car-smf.do but it doesn't look anything like their AGM batteries https://www.hankook-atlasbx.com/en/product/automotive/passenger-car.do which have a different style of handles.
3. The top of the battery has the "Advanced Seal Double Lid" per the AtlasBX SMF Technology https://www.hankook-atlasbx.com/en/technology/automotive/mf-technology.do not the "6 Valve Design" with pressure relief valves that is characteristic of AGM design https://www.hankook-atlasbx.com/en/technology/automotive/agm-technology.do 
4. You can get the battery for only $80 or $85 from a Tesla SC. That seems pretty cheap to me for an AGM battery.
5. I found this photo of a packing box that says it is SMF type.



__ https://www.facebook.com/video.php?v=2672840646333848


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## bitmanEV

I had / have 3 EVs (Zoe, Leaf & M3) and they all had ICE 12v Lead Acid batteries what's a shame because Lead Acid batteries can indeed deliver enormous amps to crank an starter motor but don't hold charge for a long period and with an EV there's no need for crank amps as there's no ICE to start
It's just cost cutting and i really do not understand why Tesla uses Lead Acid batteries for their 12v system and not uses Lithium batteries


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## pjfw8

bitmanEV said:


> I had / have 3 EVs (Zoe, Leaf & M3) and they all had ICE 12v Lead Acid batteries what's a shame because Lead Acid batteries can indeed deliver enormous amps to crank an starter motor but don't hold charge for a long period and with an EV there's no need for crank amps as there's no ICE to start
> It's just cost cutting and i really do not understand why Tesla uses Lead Acid batteries for their 12v system and not uses Lithium batteries


Lithium batteries have relatively poor cold-weather performance. Lead acid batteries are less expensive and perform well in the intended application.


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## android04

I've looked in the Hankook batteries website before and couldn't find specific info on the Model 3 battery on their lists, but didn't think downloading their catalog PDF would help. It obviously did help in finding more info, thanks for sharing. Here's a screenshot of the relevant page. The three batteries with (*1) next to them are in Teslas. The first one goes in the Model S and has a AGM in the name, the second goes in the Model X and only has MF (maintenance-free) in the name, and the third goes in Model 3/Y and also has MF in the name. So you seem to be right that our Model 3 batteries are not AGM. The question now is does it matter for longevity in our application?


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## GDN

I don't recall anyone ever claiming this is an AGM battery. That would perform better likely since there is not starter, but I don't think this claim is wide spread. Maybe I've just read right over AGM, but all of the talk I recall is why they didn't use something other than the maintenance free battery.


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## JasonF

GDN said:


> I don't recall anyone ever claiming this is an AGM battery. That would perform better likely since there is no starter, but I don't think this claim is wide spread. Maybe I've just read right over AGM, but all of the talk I recall is why they didn't use something other than the maintenance free battery.


I assumed AGM by reference, because the type recommended for the Model 3 is a "deep cycle" battery. And all of the deep cycle batteries I've found are AGM. It's very difficult to find one that isn't AGM.


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## bitmanEV

pjfw8 said:


> Lithium batteries have relatively poor cold-weather performance. Lead acid batteries are less expensive and perform well in the intended application.


Sure may be not Lithium batteries but some sealed low maintenance or deep cycle batteries would do a better job IMHO

Lots of problems with EVs are due to flat 12v batteries happened to me also


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## TomT

There are lots of lead-acid deep cycle batteries and they are very common in the marine industry. The only EV I have ever had that was not flooded lead-acid was my 2016 Volt PHEV which was AGM lead-acid...


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## JasonF

TomT said:


> There are lots of lead-acid deep cycle batteries and they are very common in the marine industry. The only EV I have ever had that was not lead-acid was my 2016 Volt PHEV which was AGM...


AGM batteries _are_ lead-acid. Maybe that's what's leading to the confusion. The difference is AGM's have fiberglass mats in them to absorb the electrolyte, making it more efficient, using less lead, and packing more into a smaller space.

Doing some research, it looks like AGM batteries' achilles heels are extreme heat and over-charging - pretty much the same things that kill Lithium batteries. Maybe if the Model 3 software would be updated to charge the battery _less_ often, or even undercharge it a little, they will last longer. After all, ICE car batteries are almost never idled with a full charge (because after you turn off the car, accessories run for a while afterward, and there is no charging with the engine off).


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## Long Ranger

android04 said:


> So you seem to be right that our Model 3 batteries are not AGM. The question now is does it matter for longevity in our application?


Yeah, good question. It may not be that significant. There's a lot more to lead acid battery design than just AGM vs. flooded. I think AGM is generally more reliable, particularly when it comes to vibration, but just being AGM doesn't guarantee more charge cycles.


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## JWardell

Seriously, seems like folks are acting like AGM means it is some advanced technology. It's just a slight update to hundreds-year-old lead acid technology which seals the battery off so it is disposable instead of renewable (frankly, a downgrade)


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## pjfw8

The 12 V battery problem is not unique to Tesla. 12 V battery failures were common in early plug-in Ford CMax and fusions, Chevy volts and even hybrids. Toyota, Lexus and Ford hybrids had 12 V failures fairly commonly in the first few years. I know this was a problem with model S and model X, especially the early years. I was not aware that it was a significant issue in model 3.


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## JasonF

pjfw8 said:


> The 12 V battery problem is not unique to Tesla. 12 V battery failures were common in early plug-in Ford CMax and fusions, Chevy volts and even hybrids. Toyota, Lexus and Ford hybrids had 12 V failures fairly commonly in the first few years. I know this was a problem with model S and model X, especially the early years. I was not aware that it was a significant issue in model 3.


I did notice that a lot of the 12 volt batteries that are only lasting 2 years are Korean brands. This whole issue might be caused by a bad electrolyte formulation - like the bad capacitors from the 90's that make any electronics from that era suspect, or the exploding LiOn batteries from Samsung. We might be looking for reasoning and workarounds for an industrial defect that might not reoccur.

But it's also possible that it is intentional, and certain manufacturers have taken a "we're not selling enough 12 volt batteries so let's build them cheaper and shorten the warranty" approach. It worked for home appliances!


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## TomT

AGMs also require slightly different charging characteristics and voltage than flooded cells...



JasonF said:


> Doing some research, it looks like AGM batteries' achilles heels are extreme heat and over-charging - pretty much the same things that kill Lithium batteries.


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## TomT

The Nissan Leaf was legendary for this! They had problems in their charging algorithms...



pjfw8 said:


> The 12 V battery problem is not unique to Tesla.


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## JoeP

in my Toyota Rav4EV (which has a Tesla drivetrain but is otherwise a Toyota) i replaced the battery with an AGM a couple years ago becuase of the self-discharge issue with non-AGM batteries. Many people who own that car (which isnt all that many, there were only 2400 made!) have done this swap.


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## bitmanEV

TomT said:


> The Nissan Leaf was legend for this! They had problems in their charging algorithms...


An easy fix was / is to remove the current limiter and an solar panel as I did with the MK1 Leaf haven't had any issues any more


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## garsh

TomT said:


> The Nissan Leaf was legend for this! They had problems in their charging algorithms...


Really? I hadn't heard of that one, and I hung out on mynissanleaf.com for many years.
My Leaf's original 12v battery managed to last the entire 6+ years of ownership.


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## TomT

I didn't have an issue either but many did and there were a number of threads about it on MNL... Biggest issue was cars that were left for many days or more. The inverter would not properly keep the battery charged over an extended period.



garsh said:


> Really? I hadn't heard of that one, and I hung out on mynissanleaf.com for many years.
> My Leaf's original 12v battery managed to last the entire 6+ years of ownership.


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## TheMagician

garsh said:


> Really? I hadn't heard of that one, and I hung out on mynissanleaf.com for many years.
> My Leaf's original 12v battery managed to last the entire 6+ years of ownership.


My experience was the same. 3 Leafs ('11, '13, '15). '11 was sold in '18 with original battery, '13 made it to 6 years and '15 made it to 5. Think that's outstanding especially since the '13 & '15 lived in Vegas most of their lives.


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## bitmanEV

https://electrek.co/2020/09/15/tesla-fix-dying-12v-batteries-software-update-musk/


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## android04

android04 said:


> I've looked in the Hankook batteries website before and couldn't find specific info on the Model 3 battery on their lists, but didn't think downloading their catalog PDF would help. It obviously did help in finding more info, thanks for sharing. Here's a screenshot of the relevant page. The three batteries with (*1) next to them are in Teslas. The first one goes in the Model S and has a AGM in the name, the second goes in the Model X and only has MF (maintenance-free) in the name, and the third goes in Model 3/Y and also has MF in the name. So you seem to be right that our Model 3 batteries are not AGM. The question now is does it matter for longevity in our application?
> View attachment 35369


That previous screenshot of the Model 3 12v battery info is from their general catalog. The US-specific general catalog has the battery info in a slightly different format (i.e. using inches instead of mm, listing the RC, and Group Size 51R). See attached pic for info on the AtlasBX MF 85B24LS


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## hammick

JasonF said:


> Doing some research, it looks like AGM batteries' achilles heels are extreme heat and over-charging - pretty much the same things that kill Lithium batteries. Maybe if the Model 3 software would be updated to charge the battery _less_ often, or even undercharge it a little, they will last longer. After all, ICE car batteries are almost never idled with a full charge (because after you turn off the car, accessories run for a while afterward, and there is no charging with the engine off).


If an AGM is not kept fully charged it will lose capacity the same as any non-AGM lead acid battery. A Maintenance Free battery just means the caps are not easily removeable to add distilled water. Next time I take the Frunk apart I will put a meter on my MY battery to see the float voltage. If the car isn't keeping this battery fully charged I don't expect to get more than three years out of it at which point I will get the Lithium one.


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## metroplex

TomT said:


> AGMs also require slightly different charging characteristics and voltage than flooded cells...





JasonF said:


> AGM batteries _are_ lead-acid. Maybe that's what's leading to the confusion. The difference is AGM's have fiberglass mats in them to absorb the electrolyte, making it more efficient, using less lead, and packing more into a smaller space.
> 
> Doing some research, it looks like AGM batteries' achilles heels are extreme heat and over-charging - pretty much the same things that kill Lithium batteries. Maybe if the Model 3 software would be updated to charge the battery _less_ often, or even undercharge it a little, they will last longer. After all, ICE car batteries are almost never idled with a full charge (because after you turn off the car, accessories run for a while afterward, and there is no charging with the engine off).


I had to comment when I found this because I used to work on battery tech.

AGM does indeed require a different temperature compensation curve and charging characteristics!
AGM falls under VRLA style batteries and yes, they use glass mats versus gel batteries. A lot of the modern smart regulators in ICE vehicles can be set for flooded or AGM.

However from experience, AGM's Achille's heel is extreme cold, not extreme heat. In fact, AGM is preferred in high temperature environments and outlast flooded lead-acid batteries in those conditions by about a factor of 1.5

In extreme cold (-40 or below), AGM doesn't tend to filter out transients as well as flooded lead-acid that is of good SOC/SOH and doesn't perform as well.

AGM was "hot" tech over 20 years ago, it was heralded as some super battery but in the end they were costing 2-3 times as much with only a 1.5 longer lifespan on average. But AGM's did a lot better in high ambient temperature environments (120F+ like the desert).


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## TomT

JasonF said:


> I assumed AGM by reference, because the type recommended for the Model 3 is a "deep cycle" battery. And all of the deep cycle batteries I've found are AGM. It's very difficult to find one that isn't AGM.


Not true. I've had many deep cycle marine batteries that were standard wet cell... My 2016 Volt had AGM and I've often wondered why more EVs did not. Perhaps cost?


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## JasonF

TomT said:


> Not true. I've had many deep cycle marine batteries that were standard wet cell... My 2016 Volt had AGM and I've often wondered why more EVs did not. Perhaps cost?


I did a google search at the time for deep cycle batteries, and they were all AGM. But I'm not willing to put in the time to call every single retailer worldwide and do an exhaustive search so that I can call one post on a message board well researched and factual.


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