battery replacement: AGM vs. EFB

I am a big fan of AGM batteries,

I recently read a post here that with minimal adaptation, you can put an Odyssey sized battery in your crv. It was something as simple as buying a wider battery tray and tie down strap.
If you do a search, you can probably find the specifics including part numbers

EFBs are for high start count applications... like auto/start stop, but at flooded cell prices. AGMs are also suitable for high start count applications. Your CRV though just needs raw power, not high start count ratings.

Upgrade to an H5 (Group 47 battery). Cosco sells an AGM version for about $170 and I can confirm it is a beast. They sell a flooded version too, but I personally would say for the limited cost difference go with the AGM. My local costco stocks the AGMs much more so than flooded cell versions (and I doubt the costco flooded version is EFB, but I am not positive).

I have not specifically checked. but an H5 should fit, and it's only a question of if you need a different tray and hold down bolts (which would be a stock item now since with the 2020 CRVs Honda moved to H5s in CRVs).

And by beast, I mean the Interstate H5 AGMs are at full charge reading well over 750 CCA, and an impedance of about 3.5 mili-ohms. I used one as a replacement recently in my 2018 Accord (which uses H5s, by spec) and the battery voltage under normal parasitic drain loads only drops about 20mv per 24 hours which is amazing at a 50 ma normal parasitic drain rate. So this is more than sufficient battery for a CRV, even with your added accessories.

@inee : Can you confirm if the Costco Interstate battery (Item#: 852210) you got is an non-AGM battery (just a regular flooded battery)? If that's the case, I guess I probably should be careful about ventilation when charging it, as it can emit gas, right? I'm also assuming that it may not be a good idea to leave the V charged overnight when you have a EFB battery? Thoughts? Thanks!

Anecdotally speaking, I have an AGM in my Miata and a regular battery in my CR-V. My Miata can still start at a lower resting voltage (11.5v) and typically holds a charge longer than my CR-V. They both have the same remote start (Drone Mobile) with LTE, so there is some drain due to that system running while cars are off. My CR-V needs to be at about 11.8v to start reliably; anything less and I have to jump it.

I've gone in both pro AGM and Anti over the past few years. Have to replace a battery on wifey's Volvo. Its getting a Napa wet battery with longest available warranty. AGMs don't like sitting around losing charge and she doesn't drive it enough.

Hope this isn't getting too far off the topic, but ... I happen to own a Subaru Forester in addition to the various Honda cars in my family's fleet. There is an interesting post on the Forester owners site right now where some engineering-types are essentially advocating that one should replace the type of battery in their car with the same type as the manufacturer put in it. In other words, if the car came with a basic FLA battery, replace it with a FLA battery. If it's a EFB, replace it with a EFB. Replace AGM with AGM. Don't mix. I'm no engineer, but if I understand the logic I'm reading, it's based on a belief that car's charging system will be tuned (my choice of words) to the battery type, and that it may not necessarily best support a different designed battery. Especially in areas of the country that experience high heat. This discussion was started by someone who was looking to replace a Subaru EFB with an AGM simply because AGM batteries are so much easier to find & buy on the market these days. Plus Subaru dealers apparently want close to $500 for their branded battery in some areas. Auto start/stop is also very common in Forester cars.

Anecdotally many have jumped onto that Subaru post saying they've not had problems when replacing their EFB with AGM batteries. Still I am left wondering if there may be some merit to the premise of replacing a battery with the same type. I assume there is a reason my NOCO 5 smart charger has a special switch setting for use when charging AGM batteries vs charging regular 12V batteries. Plus, I have experience using the NOCO on 2 AGM batteries I own. Several years ago I put an AGM battery in my son's 2014 Outback because at the time the store was out of stock of the basic FLA battery spec'ed for his car. I also have an AGM battery in my riding lawn mower. It died after just 2 years and the mower dealer recommended that I keep the replacement AGM battery on a charger during the winter months. Whenever I have used the NOCO charger on those 2 AGM batteries, the charger reaches full charge within 15 to 30 seconds. I mean it, literally that fast! Even when my battery tester says the AGM battery in the son's car needs "recharging." 30 seconds later it is fully charged. And I've rechecked with the battery tester to verify the full charge because I was in such disbelief. I've never run that NOCO charger longer than that on either of those 2 AGM batteries. If I use it on the CRV or my Pilot with their basic FLA batteries, it may charge for 2, 3, or more hours before reaching the single green light full-charge level. So I guess I'm left wondering if in addition to all the design advancements of an EFB or AGM battery and their higher technical specs, like CCA and so on, if there is another equally important consideration to keep in mind. Namely, the car's alternator and charging system's ability to support that type of battery. Or am I making much ado about nothing? Thanks.

Just curious, I suppose that EFB is just an enhanced flooded battery, so when charging it, it would still emit gas and may not be a good idea to leave it charging in the garage overnight (when your garage is connected to living room and bedrooms etc), right? Thanks!

@williamsji : I'm using a NOCO Genius 1 to charge my AGM battery and the green light is slowly blinking (not solid light). What does that mean? Thanks!

Last general comment on batteries here: Seasonal temperatures DO affect how NOCOs setup and apply a charging cycle on a battery. So keep that in mind. I expect other brands of smart chargers follow a similar approach, as this is not rocket science, just basic battery chemistry at work.

There are a couple of reasons for this:

1) As ambient temperature declines, chemical activity in a battery also slows. What this means in terms of charging is that a smart charger will adjust the rate of charging downward as temperature drops. In other words, in cold ambient temperatures (think 30 degrees F and lower) the maximum charge capacity of a battery declines, as does the rate at which it will accept charging current.... so a smart charger accounts for this in it's charging functions. CCA will also decline with ambient temperature as well, which is why while it is generally heat that degrades batteries fastest, the cold makes batteries much more energy sluggish, and that gets tested on an engine start stress. This is one key reason owners see more "failures to start" in cold weather than in warm weather.

2) a motor vehicle battery can store more energy in the form of stored charge at warmer temperatures. Hence expected charging behavior and charging times will change for smart chargers depending on ambient temperatures. Warmer temperatures also activate the electrolyte better, which means you may also see higher voltage readings from the same exact battery in very warm conditions compared to very cold conditions. Obviously.. how long a vehicle sits between drives adds additional factors to this.. because days sitting parked in low temperatures means you have very cold battery internals, which will then begin to warm some when you drive the vehicle or smart charge the battery.

So, one of the comments referred to the alternator as being "tuned" for charging the type of battery that was installed as the original equipment on the vehicle. I believe this is both true and not true at the same time. I don't think the "alternator" is tuned to the battery type but the charging circuit is. I believe it is the ECM computer that directs the level of the output of the vehicle alternator. Honda (like many fuel-efficient cars) "senses" the voltage potential of the battery and when it reaches a certain level of voltage potential, it switches the alternator output voltage to a lower level. This is sometimes referred to as "dual output charging mode" and this is where the difference in battery types matters (e.g., AGM vs FLA batteries).

The general characteristic of an AGM battery is that they can accept a slightly higher saturation charge than an FLA battery (like 0.5v higher). They also can be charged faster (meaning they can accept a higher charging current), assuming they are not in a "cold" state. Note: batteries "warm up" during the charging process, as an AGM warms up it can accept higher charging currents. This faster charging profile is due, in part, because they have lower internal electrical resistance within the battery structure. But if the computer was programmed to assume that is charging an SLA battery, it may switch the alternator output to the "low output mode" before the AGM has reached its full saturation charge potential.

How does the computer determine if the battery is fully charged? It "senses" the voltage potential of the battery. The saturation charge of an FLA in terms of voltage potential is a little lower than an AGM so, in theory, the computer will switch the alternator output to low output mode (which means that the alternator output is not enough to run the vehicle AND charge the battery at the same time. Actually, with modern vehicles having so much additional electrical load beyond simply running the engine, if the engine RPM is low (e.g., at idle) it is entirely possible that the vehicle is consuming more electrical power than the alternator is putting out. Honda actually warns owners in the owner's manual about this possibility.

So how do you fix this problem of the alternator being switched to low output mode before an AGM battery is fully charged? You would have to change (raise) the voltage level potential that is being "sensed" at the battery such that the computer does switch the alternator output to low mode too soon.
How can you do that on a Honda? One way is to increase the electrical load by turning on your headlights. But that is sort of counterintuitive because you are putting more load on the electrical system just so you get a small additional charge on your battery.

Another way (in my mind, a better way) is, if you switch to an AGM battery, slightly increase the battery voltage level sensing that causes the alternator to switch to low output mode. How can you do that? On a Honda, I don't know the answer. On a Toyota, the is a simple hack you can do: "...adding a resistor (Diode) to the Alternator's feed-back sensor circuit, at the 7.5A S (for sensor) fuse" There is a fuse for the battery sensing circuit in the fuse block under the hood on the right side. You can swap the fuse for a GM diode that has a similar shape to the fuse (you have to grind or sand a little metal off the diode tines that plug into the fuse slot to get a good fit). This diode changes the sensing circuit from 13.9V to approx. 14.5V hence delaying the switch to low charge mode. This is what some Toyota/Lexus owners do when they want to switch from the stock FLA battery to an AGM battery and want to ensure the battery is fully charged.

If there is someone on this forum who may know of a way to change (or delay) the Honda method of sensing when to switch to low output mode, I would be very interested in hearing that.

In general, switching to a good quality AGM battery should result in a longer life of the battery simply because the increased duty cycle (about 200%) of AGM's vs FLA, (...although YMMV). But I don't know what the longevity effect of not being able maximize the charge on AGM. Obviously, you could manually maximize the charge by using a smart charger say once a week or month but that seems like a lot of trouble versus simple hack that we use on the Toyota charging sense circuit. Although, some people say maximizing the charge on an AGM is not actually for the longevity of an AGM. For more information about the Toyota AGM battery switch and increasing the charging voltage, search for the toyota-4runner.org and look for "291105-raising-alternators-voltage-properly-feed-your-agm-battery".

The last post is 9 months old and your post is very specific. Please start a new thread on this. Closing this one now.