Tell me about AGM batteries

[toyodaaddict]

I need a new battery for my 1980. I was looking at this Super Start AGM $210 on sale. https://www.oreillyauto.com/detail/c/platinum/more-powersport/battery---automotive/battery---optional/d6cf089e3164/super-start-platinum-battery-group-size-34/ssbq/34plt
I have never used an AGM battery but have seen that alot of you do, and recommend them.
While looking into it, I fell into a rabbit hole of people saying our older charging systems are not designed for AGM and are not up to the task of keeping them properly/fully charged. Saying they will fail prematurely because of this and blah blah blah. So what can you guys tell me about this? Will the AGM perform/last in my truck or should I just go with another costco interstate and save $100?

[toyodaaddict]

 This was posted on a jeep forum.

Can a Car Alternator Charge an AGM Battery?
Post author
By OP
Post date
April 3, 2021
In an earlier article, we discussed how well different types of line-input chargers are suited for charging AGM batteries. The conclusion was that what is needed is a smart charger – preferably one with a dedicated AGM mode.
But what happens if you put an AGM battery into your car? There the battery is not charged from line power, but by the alternator. Can the car alternators charge AGM batteries?
In this short post, I will try to shed some light on the issue. In a nutshell, the alternator-based charging systems in most cars are intended for flooded lead-acid batteries, and will not work optimally with AGM batteries. With the default charging profile, these systems risk both over- and under-charging an AGM battery, which is much more sensitive to charge voltages and staging. The charge controllers in newer vehicles may sometimes be reprogrammed to work with an AGM battery.
We're next going to look at the important job of the regulator, the exact problems of charging AGM batteries with the alternator, and when a car charging system may be compatible with AGM batteries.

Regulator is key
Car battery charging is actually controlled by a combination of the alternator and a regulator. The regulator's task is to cap the output voltage of the alternator to a safe level both to prevent damage to car electronics and to avoid overcharging the battery during long high-RPM drives.
The positioning of the regulator varies: in some cars, the regulator may be integrated into the alternator and be inside its casing; in others, it may be an external component. In newer car models, the regulator is usually incorporated into the engine control unit (ECU) and has more advanced functionality.
Regardless of the position, it is the regulator or charge controller that sets the charging voltages, limits the charging current, and in more advanced systems, controls the charge staging.

Problem 1: Low absorption voltage
Many regulators have too low output voltage to properly charge an AGM battery. Typical regulator setpoints are 13.5V to 14.4V. These voltage levels are enough for most of the bulk charge stage, but a bit too low for a proper absorption charge, which would take a voltage between 14.2V and 14.9V depending on the temperature and the battery model. For more info, see my articles on AGM charge staging and voltages.
On a typical car charging system, an AGM battery will therefore charge slow, and never quite to 100%. This will cause fast capacity fade and lead to a short battery life.

Problem 2: No float stage
An another shortcoming of conventional alternator & regulator car charging systems is the lack of float charge stage.
For best performance and longest battery life, AGM batteries should be charged full with a high absorption voltage between 14.2...14.9V, with the exact voltage and time depending on temperature and model (see previous article).
After this, the charging voltage should absolutely be dropped to a lower level to prevent overcharging. This lower voltage stage is called float charge, and has recommended voltages between 13.5...13.8V, again depending on temperature and battery model (details in previous article).
This drop to float stage is missing altogether in many older car charging systems. If an AGM battery is installed to such a car, there is a high risk of battery overcharging on long drives.

No drop-in compatibility
We've seen that the output voltage of car regulators is often an unhappy medium for AGM batteries – too low for absorption, too high for float. Low regulator voltages around 13.5V are pretty good for floating AGMs, but will never charge them full. The higher regulator outputs of 14.4V are still a bit low for proper absorption voltage, but much too high for float.
Because of the mentioned issues, an AGM battery is not a general drop-in replacement for a conventional flooded-cell lead-acid automotive battery.
The issues you face if you substitute a flooded unit for an AGM depend on the car model and your use profile. In some happy cases, a combination of short typical journeys and a high voltage setting mean that the battery will work just fine.
In others, the over- or undercharging will lead to fast capacity fade, and you need to replace the battery prematurely.
Some newer vehicles may be smart enough to automatically detect the new battery type through load testing and adjust charging accordingly. In this case, you will face no issues – except for the possible warning messages of unauthorized battery change from the on-board computer.

Compatibility by reprogramming
In many new vehicles with an engine control unit (ECU), the battery charge profile is a matter of charge controller programming. Such cars may allow you to swap the original flooded-cell lead acid battery for an AGM model if the charge controller settings are updated accordingly.
Before purchasing an AGM battery for your car, make sure that your car's charging system is compatible with AGM batteries, and the ECU is appropriately programmed to recognize the battery type. As so many other things in modern cars, this is something you will likely have to leave to an authorized service center.

Flooded lead-acid more tolerant
Some claim that AGM batteries actually are a drop-in replacement for flooded lead-acid units in car applications, because the optimal charging voltages for the two battery types are not all that different.
There is some truth to this claim: the optimal absorption and float voltages of flooded lead-acid and AGM batteries are indeed within 0.2V or so: typical values are 14.7V/13.6V for AGM and 14.5V/13.4V for flooded.
However, this claim misses an important point: an AGM battery is much more prone to both under- and overcharging than a regular flooded lead-acid battery. Specifically:
AGMs suffer much more from insufficient absorption charge
AGMs are more sensitive to overcharging
So while the crude charging profile of a car alternator & regulator combination is not really optimal for either battery type, AGMs suffer much more from the deficiencies.

This video talks about some of it, if you dont want to read the wall of text https://youtu.be/GfJfBnyZEWM

[mudmaster]

My first gen never had an issue keeping my yellow top charged.

[a1gemmel]

I've had a red top for over 2 years and it's fared just fine. I also run a fridge off it for camping trips.
Two anecdotal brags of quality:
- discharged it to 2 volts last year accidentally leaving the fridge plugged in for a few weeks while it sat, recovered it with my stick welder and it's had no problems since
- later, alternator broke on a trail 80 miles from home, finished the trail and drove it home at night (halogen headlights) with no charging system and it only dropped to 11.8 volts.

[toyodaaddict]

I know a friend had good luck with a yellow top in his samurai but it was before people started complaining about optima. Another friend recently had a red top only make it 3 years in a YJ.

I'm going to stick with a standard battery this time. I'll save $100. Dont really need an AGM, mostly interested in lack of corrosion. I was looking at a budget one anyway, not looking to spend 3-$400. Sales over. Maybe I'll know more and try one next time

[Cheesemaker]

I had a standard battery in my truck for over 7 years, and I just replaced it with the same battery.  It was starting to start a little slower.  But I use those felt washers, and the battery terminal spray.  My batteries never corrode.  Just spray them down when you change your oil, and all is good.

[Gnarly4X]

I had a standard battery in my truck for over 7 years, and I just replaced it with the same battery.  It was starting to start a little slower.  But I use those felt washers, and the battery terminal spray.  My batteries never corrode.  Just spray them down when you change your oil, and all is good.

Yes... I agree.  I also use the felt post washers and spray with a battery terminal protector.

Periodic maintenance is important for longevity and avoiding the dreaded "suddenly dead syndrome".

How the battery is used makes a difference in longevity.  Excessive draining will shorten its life

An alternator that is continuously overcharging can also shorten the battery life.

My DieHard Gold battery in SoCal lasted 7 years.  Here in Arizona batteries don't seem to last that long, typically 2 to 4 years.

I also do periodic maintenance.  Clean the cable clamps and terminals, wash it down with a baking soda solution, check the specific gravity with a hydrometer.

The batteries with no cell caps (sealed) cannot be fluid checked, so don't buy those unless I have no other choice at the time of purchase.

I have never owned an AGM battery so I have no experience with those.

Gnarls.

[OVRAROK]

I run 2 oddessy pc1200mj, pc1200lmj in engine compartment ran in parallel, and a 3rd 100aH AGM in bed area running off 50 amp dc to dc charger with solar. The oddessy are pushing 10 Years. Also running 165 amp alternator. All battery cable are 0 gauge. Have the " big 3 " upgrade on negative cables in 0 gauge.
I also have an oddessy battery charger/ conditioner
Alternator has been reworked to kick on at 1100 rims
I'm running winch, rock lights, pod lights, fridge, portable bun trail welder. Never had any issues with charging. With solar panel hooked up, I've had fridge running for 3 weeks without starting 4runner. The dc/dc charger will charge 3rd battery, when fully charged. Solar will trickle charge 2 starting batteries.

[Cheesemaker]

My wifes car has a AGM battery, but it has the start stop technology.  Which I am not a fan of.  Especially, when you are taking off on gravel onto pavement.  I have figured out that if I let off the brake a little, the engine will start back up, and then I can take off easier on gravel.  The car is a 2019 Malibu, and it still has the same OEM battery. 

The AGM's are more of a Deep Cycle style of battery, and since they don't gas, you can mount them anywhere.  My sons Cruze has his mounted in the trunk. 

[toyodaaddict]

I had a standard battery in my truck for over 7 years, and I just replaced it with the same battery.  It was starting to start a little slower.  But I use those felt washers, and the battery terminal spray.  My batteries never corrode.  Just spray them down when you change your oil, and all is good.

Looks like I got 7 years also. The date sticker says 5/15.  It was a costco interstate group 34. It was working fine until the day it wasn't. Stone cold dead, reading .6 volts I think it was.

[toyodaaddict]

I dont know anything about battery chargers but I'm thinking about trying this https://no.co/genius5. Looks like I can use it as a charger and tender, with standard and AGM batteries. My current charger is an old garage sale purchase and I was thinking about getting a tender anyway.

I'm still tempted to try an AGM at some point, just to see for myself how it works.

[D3vilduck]

I have two X2Power Premium AGM batteries from Batteries Plus in my crawler and Tacoma and they've been great. They fire up better than any other battery I've had. My Tacoma seems to kill batteries a little early most likely from vibration of running desert roads but so far, so good...and they don't crud up. Anyway, I thought I was going to jump on here to show you a good deal with a great replacement warranty but looks like the prices went up.

It looks like East Penn Manufacturing Co, Inc. is the current owner and manufacturer of Duracell batteries and their AGM battery is at a decent price. You can get 10% off Batteries Plus by signing up for their newsletter, too. Then unsubscribe later...

[Cheesemaker]

For me, Les Schwab Tires has the best price, and warranty hands down, vs. any other name brand ones. 

And several buddies are buying up this battery charger off Amazon.  And swearing by them.  https://www.amazon.com/dp/B07QPSNZPP/ref=cm_sw_r_cp_apip_3qzy97HnpcdJy/url