[ForesterBill]

That works great until you are stranded with a dead AGM and call roadside assistance for a tow. My son has seen this on multiple occasions. Cars towed in with a dead AGM that should be equipped with an EFB.

Based upon dead battery complaints that I have read on this forum and elsewhere, I bet a lot more Subarus are towed in with dead factory EFB batteries than AGMs!

 

[Fibber2]

Nobody is saying that an EFB won't die. All batteries will. The questions is:

1) Which battery will last longer in a hot engine compartment Start-Stop (enabled) and actively used vehicle? If there is no thermal sensor gating recharge, it has a charging algorithm that cannot be adjusted for the different battery type used (some of the European brands reportedly have that ability as part of the battery registration process) and no thermal barrier to give the battery a break so that it CAN recharge safely - the literature suggests that the EFB may last longer.

2) If Subaru only supports safe charging of an EFB, will they be of any help should you go to the dealer (driven in or towed) and ask for charging system diagnosis and possible service if you have an AGM battery in residence? The evidence is suggesting that they might be justified in saying no.

Oh and as a data point, my terminals on a 4+ year old 2019 OEM EFB look great. The Subaru waxy protector is still intact and no visible corrosion.

 

[bman400]

Oh and as a data point, my terminals on a 4+ year old 2019 OEM EFB look great. The Subaru waxy protector is still intact and no visible corrosion.

Where do you live? I suspect the fuzzy acid that forms maybe related to HEAT. I lived in Vancouver, BC for most of my life until 2001 when I moved to TX. This was my first experience with dealing with high battery heat that created the fuzzy acid. Never had it happen in Vancouver. I previously owned a 1992 Honda Civic, and never had to deal with this acid fuzz.

I have to wonder if the heat causes the Flooded/EFB batteries to produce more acidic expulsion and therefore generate for acid fuzz?

 

[bigbird1]

That works great until you are stranded with a dead AGM and call roadside assistance for a tow. My son has seen this on multiple occasions. Cars towed in with a dead AGM that should be equipped with an EFB.

Everyone is free to do what they like but they should be aware of the potential consequences.

I think you, me, and anyone else posting on this thread is smart enough to know when their battery is going south.
We are all proactive here.
The typical owners out there wouldn't even know or care what an AGM or EFB battery is.
When their car won't start, they just phone roadside assistance or get a tow into the dealership, which will replace the dead battery with whatever battery they stock.

 

[bman400]

I want to throw into the mix another battery type that I have investigated for my 2013 Nissan Leaf that would be applicable here as it supports and likely works better with the Subaru Charging System far better than AGM. It's called LiFePo4. They have a built-in BMS(Battery Management System) to allow charging from regular alternator/charging systems.
On the plus side:

• Lighter
• Handle Deep Cycle discharge very well.
• Crazy amounts of CCA for all the guys up north.

On the minus side:

• Expensive, easily > $300-$400
• BMS Prevents charging below certain temperature.
• Due to being smaller requires slight mods to make the battery fit, ie new tie down, extra spacers.

 

[FelineFreddie]

Based upon dead battery complaints that I have read on this forum and elsewhere, I bet a lot more Subarus are towed in with dead factory EFB batteries than AGMs!

According the the recent battery settlement case against Subaru…

Home | In re Subaru Battery Drain Products Liability Litigation

If you bought or leased certain Subaru Vehicles, you may benefit from a class action settlement

www.subarubatterysettlement.com

“You are a Settlement Class Member if you are a resident of the continental United States, including Hawaii or Alaska, who currently owns or leases, or previously owned or leased, a Settlement Class Vehicle originally purchased or leased in the continental United States, including Alaska or Hawaii. The Settlement Class is not intended to exclude military personnel stationed overseas. Settlement Class Vehicles include model year 2015-2020 Outback, 2015-2020 Forester, 2015-2020 Legacy, 2015-2020 WRX, and 2019-2020 Ascent.”

Many of these vehicles were delivered exclusively with EFBs.

EFBs are not immune to problems. There may be numerous, completely valid reasons to use an EFB, but avoiding a dead battery isn’t one of them…

 

[Fibber2]

@bman400 - How many EFB's have you seen grow fuzz? I can understand the issue with basic Flooded Cell batteries, but a good EFB should be pretty resistant to the problem. And honestly, is this such a big issue even if the EFB wasn't quite perfect in the fuzz department that it should be tossed in favor of a battery that might be incompatible with the Subaru charging system? But to your question, I live in NY, between NYC and Albany.

Maybe the problem isn't with the concept of an EFB, and that another EFB may very well be the preferred choice given the limitations of the vehicle. Maybe we need to look further.

1) All batteries are not created equal. People have been railing against Subaru OE batteries for as long as I've been a Subaru owner (since 2001). Would I want another Panasonic? Maybe not. From what I've read, I think I'd love to try a Yuasa ISS Q85. It seems to be a powerhouse, and some of the tech stuff I found in their literature sounds like they might know how to do it right.

2) We don't know if Subaru went too far in their smart charging algorithm. If the battery is habitually undercharged (any battery!) it won't fair well long term. There are things that can be done to encourage higher charging voltage on these new systems.

3) Realize that Subaru is in a bit of a bind. If EPA rating is dependent on all these fuel saving gimmicks, then changing anything of substance becomes a huge deal. It becomes cheaper to hand out free batteries than to address the real problem.

 

[Fibber2]

LiFePo4 has potential, but again needs a compatible charging system. They can be discharged (start the engine) at low temps, but they don't like to recharge at sub-freezing temperatures. If you live where the daytime temps don't make it to 20F (as it did here two weeks ago), this wouldn't be a good choice without some more sophisticated power management.

 

[Fibber2]

Based upon dead battery complaints that I have read on this forum and elsewhere, I bet a lot more Subarus are towed in with dead factory EFB batteries than AGMs!

I think you realize that the above is a meaningless statistic, even though it is true!

The question at play is whether Subaru has any obligation to assist you with any level of diagnostics if you change fundamental battery technology. This isn't a Magnuson-Moss Warranty issue here. If I put in a Yuasa or Duralast EFB, Subaru would be very hard pressed to deny me coverage for an electrical system issue. An AGM replacement? They'd have a case based on what I've been reading that there are incompatibilities under some operating conditions.

 

[FelineFreddie]

In a way, this issue of AGM .vs. EFB choice may become, in part, self-resolving, as more aftermarket EFBs become available and the pricing differential moves more in balance.

The 12 volt battery in my Solterra is a LN1-MF battery, which is an EFB. So, the use of EFBs is expanding, which generally seems to imply a higher market availability in overall supply of that form of battery construction.

 

[bigbird1]

Those Lithium-Iron-Phosphate batteries are great for motorcycles that never see sub-freezing temps.
But for a car in any environment outside the deep south, I wouldn't bet on it.
And as stated, they need an expensive Battery Management System,

 

[Black21Limited]

My personal experience with flooded (automotive) batteries has been that terminal corrosion is much more improved over the flooded batteries of 25+ years ago.

Perhaps it might be due to the voltage regulator not being in the alternator, or stand alone on the firewall/inner fender.

PCM/ECU controlled alternators seem to do better overall, (as far as for the type of battery supplied with the car, or available profiles that match battery type) given they use more than just one basic target voltage. So cleaner terminals may be the result, along with better battery designs.


As far as pushing current into an AGM in a hot environment, that would probably be more the case with city use and AS/S.

For primarily highway use, the only time higher current is going to happen is directly after the initial start up. After that there should be relatively minimal current flowing into the battery. And there will be plenty of air movement at highway speeds.

So an AGM could do better in an EFB charging environment, if you don't do a lot of idling etc. with higher current demands where the charging system cannot keep up, and the battery has to make up some of it. Or all of it in the case of AS/S when it is in Stop Mode then Start Mode.

 

[Fibber2]

And that fits with my previous statements. If you disable the SK Start-Stop system then you aren't taxing the battery all that much more than the SJ Forester did. You probably still have a different charging algorithm in an SK with S-S defeated than you had in an SJ Forester, because you can't change the fact that the electrical engineering team set things up differently when transitioning from a traditional flooded cell battery to an Enhanced FB. But it's probably not all that harmful to an AGM battery given the low load. Buy whatever battery makes you smile, provided you are willing to put up with whatever Subaru might say if you happen to need them.

But if you have S-S enabled and use it, I think the case has been made for replacing the EFB with another EFB. As @FelineFreddie said, hopefully the supply choices and pricing of EFB will fall into line in the near future.

 

[boureesub]

An area where EFB greatly outperformed AGM was in temperature tests. AGM batteries tend to lack thermal stability, which leads to shorter battery life in high temperatures.

I've read this elsewhere and believe this is in reference to the potential for excessive gas generation and possible runaway that can occur at higher temperatures. How does one reconcile this statement with the improved life (AGM vs flooded) experienced by folks who drive in hot climates? Does the statement apply only to AGMs operated in a stop/start manner? A frustration I have with white papers like this is they offer conclusions with little supporting data to provide context.

 

[Fibber2]

I've read this elsewhere and believe this is in reference to the potential for excessive gas generation and possible runaway that can occur at higher temperatures. How does one reconcile this statement with the improved life (AGM vs flooded) experienced by folks who drive in hot climates? Does the statement apply only to AGMs operated in a stop/start manner?

From my reading I believe it can be reconciled as follows:

1) Almost every anecdotal case you've ever heard has been comparing STANDARD flooded cell batteries to AGM batteries. And I'd tend to agree. AGM wins. Why? Standard batteries are relatively old tech. The plates are thin, the chemistry basic, no separators so the sulfate easily. Cheap to produce, but generally good value for the low cost to buy. The demands aren't great on them, with limited intentional deep cycling. Add in an accidental deep cycle or two, and a standard flooded battery is toast. An AGM can take it.

2) Start-Stop micro-hybrid changes everything. True EFB (not Advanced or Robust SLI flooded cell) is a very different animal. Thick plates, fiber separators, chemical additives - all change the outcome. Now add in advanced charging algorithms customized to the exact chemistry of the battery, it's preferred charging curve (voltage/current/temperature), whether you control temperature or not and how you apply the charging as you intentionally deep cycle the battery every single day and often leave it intentionally undercharged. NOW compare EFB to AGM and see if you see a stark advantage. The literature says EFB might just win.

 

[Fibber2]

@boureesub: One of my big frustrations while researching this is my inability to always obtain full manuscripts of papers from conferences and journals. There is a lot of amazing stuff out there, but as a retiree, I no longer have unlimited tech library access and translations as I did while working. I'm still publishing so get some comp access and I have some back doors for advanced searches and databases, but there are limits.

If you have unfettered access, research studies on Dynamic Charge Acceptance in reference to AGM & EFB thru sample charge/discharge cycles (like 1 km city cycles) and long term life cycling. Look at battery registration and how it changes the I/V/T curves depending on the capacity of the battery, the chemistry of the battery (gel vs EFB vs AGM), aging of the battery. As Subaru lacks user battery input, it's likely set and customized for the battery they supply - namely an EFB. But I wonder if SSM4 has any provision for change? Read up on what happens if you apply the wrong battery characteristics. There are some authors with interesting papers, such as Eckhard Karden from Ford Research Germany. And of course follow those whom he quotes in the papers that he references.

White papers provide great high level summaries. But if you don't like white papers, go do the heavy lifting and find the sources of the data, as I did. Then if you disagree with my conclusions, come back and lets hash it out.

 

[auntiesuebee]

This is all interesting reading but at the end of day it boils down to a simple fact. Subaru has engineered it's current fleet of vehicles with AS/S to use an EFB and when the EFB fails, as all batteries are prone to do, it should be replaced with another EFB.

The challenge is the limited availability of replacement EFB's in the US and Bozo's Battery Warehouse not being aware that you can't swap an AGM for an EFB in a Subaru.

 

[Fibber2]

I know it may sound strange, but at the moment I'm in agreement with you @auntiesuebee ! Imagine that....

We've been brainwashed that AGM is better, but if you follow the data it reads that EFB is technically the right choice for a current Subaru Stop-Start vehicle. Knowing what I known now, I'll be shopping for another EFB as I'm nursing my 4 year old battery along.

But I still think that at least some of us have a lot to explore. Reasons?

1) A growing number of vehicles are going out of warranty, so people can experiment as they please.
2) Some owners disable Stop-Start, greatly reducing the load and thus change the depth of discharge.
3) We may discover that Subaru has provisions for shifting the charge profile built-in and changeable thru SSM4.
4) The aftermarket may step up and provide charge program shift to accommodate AGM.
5) Or, someone from SOA might assist and it might not be as hard as we've made it out to be.
6) In the meantime, hopefully prices of EFB will drop / availability will rise to make it a good economic choice too.

Even if EFB is the best choice, my experience so far is telling me that the system is so biased towards fuel economy that the battery is being starved. I should probably drive for a day with a recording voltmeter to see the whole cycle, but my battery seems to be well below 12.4v too much of it's life. I might force the issue with my dealer and at least get a fresh battery out of this and get the charge system looked at yet again.

 

[bman400]

Even if EFB is the best choice, my experience so far is telling me that the system is so biased towards fuel economy that the battery is being starved. I should probably drive for a day with a recording voltmeter to see the whole cycle, but my battery seems to be well below 12.4v too much of it's life.

I bought the AntiGravity Battery monitor. It attaches to the battery terminals and records as your drive. You then use an APP that Bluetooth with the recording device and you can then display what the vehicle is doing with your battery. I bought for my 2013 Nissan Leaf because I was trying to find out how/why the 12v battery was dropping down to 11.8-12.1 volts. And it basically record the Nissan Leaf was being extremely frugal with wanting to charge the 12v. Short answer it rarely tries to charge the 12v.

 

[Fibber2]

I had a chat with the AntiGravity folks. Data acquisition is every 2 seconds. I was hoping to be able to chart vs the clock (time domain) so that I can easily track against driving and stop-start events, but will have to do that manually. Biggest issue is they say there is no export mode, so I can't move the data in a standard format from their phone app to a PC for more serious analysis. So a useful tool but not as full function as I would have liked. I need to think about this....

So I got bold today. I wrote to Dr. Karden at Ford. Let's see if he is willing to weigh in on a Subaru application and if perhaps he has any technical contacts there.