Does an AGM battery make the alternator work harder (older cars not originally equipped with an AGM battery)?

[Zack1978]

Hi everyone,
I have a quick question about utilizing an AGM battery in a car that was originally equipped with a wet battery. As has been discussed here, an AGM battery charges differently than a wet battery in that it potentially needs more power to achieve a state of full charge.
At this point many vehicles that are on the road were not engineered with AGM batteries in mind and neither were their alternators.
I have read some conflicting information that an AGM battery taxes the alternator to a greater degree to achieve a full charge status. The additional charging requirements thus shorten the life of the alternator because it is being forced to run at it's maximum duty cycle for the majority of the time.
A car built from the start with an AGM battery has an alternator appropriate for the unique charging needs.
Is there any truth to this theory? Does anyone have any real world experience with this idea?


Thank you!

 

[Rand]

Short answer, No.

Hi everyone,
I have a quick question about utilizing an AGM battery in a car that was originally equipped with a wet battery. As has been discussed here, an AGM battery charges differently than a wet battery in that it potentially needs more power to achieve a state of full charge.
At this point many vehicles that are on the road were not engineered with AGM batteries in mind and neither were their alternators.
I have read some conflicting information that an AGM battery taxes the alternator to a greater degree to achieve a full charge status. The additional charging requirements thus shorten the life of the alternator because it is being forced to run at it's maximum duty cycle for the majority of the time.
A car built from the start with an AGM battery has an alternator appropriate for the unique charging needs.
Is there any truth to this theory? Does anyone have any real world experience with this idea?

 

[jetman]

Hi everyone,
I have a quick question about utilizing an AGM battery in a car that was originally equipped with a wet battery. As has been discussed here, an AGM battery charges differently than a wet battery in that it potentially needs more power to achieve a state of full charge.
At this point many vehicles that are on the road were not engineered with AGM batteries in mind and neither were their alternators.
I have read some conflicting information that an AGM battery taxes the alternator to a greater degree to achieve a full charge status. The additional charging requirements thus shorten the life of the alternator because it is being forced to run at it's maximum duty cycle for the majority of the time.
A car built from the start with an AGM battery has an alternator appropriate for the unique charging needs.
Is there any truth to this theory? Does anyone have any real world experience with this idea?


Thank you!

No

 

[Gus_Mahn]

Hi everyone,
I have a quick question about utilizing an AGM battery in a car that was originally equipped with a wet battery. As has been discussed here, an AGM battery charges differently than a wet battery in that it potentially needs more power to achieve a state of full charge.
At this point many vehicles that are on the road were not engineered with AGM batteries in mind and neither were their alternators.
I have read some conflicting information that an AGM battery taxes the alternator to a greater degree to achieve a full charge status. The additional charging requirements thus shorten the life of the alternator because it is being forced to run at it's maximum duty cycle for the majority of the time.
A car built from the start with an AGM battery has an alternator appropriate for the unique charging needs.
Is there any truth to this theory? Does anyone have any real world experience with this idea?


Thank you!

I think the point of an AGM battery is that it lives better at a lower state of charge. Fuel efficiency increased by reducing the parasitic drag caused by maintaining a high state of charge and high battery voltage. That being said, my '15 AGM equipped Auto S/S F150 has been operating for three years with the current sensor disconnected which disables Auto S/S and charges by voltage instead of state of charge. No issues to report, but it won't get another AGM when the time comes to replace the battery.

 

[3800Series]

I've used them for years, they have been my replacement of choice for anything. In my younger years I was always having problems with batteries and having to ask folks to give me a jump start. Just young and poor so I had to work with what I had and some times that meant a dead battery after I got off work in winter.

That said I now value batteries a lot so I'm far more willing to spend the premium to not have to relive those days. I've used several AGM's and as said my go to of choice. As far as I am aware all modern cars can read the batteries voltage, so they will only charge until a certain point. AGM is a lead acid battery but for simplicities sake traditional batteries have a slightly lower full charge, the alternator will only charge until this point for AGM's though some will charge at a higher voltage 13.2v-13.5v while it is not uncommon for some to charge up to 14.5v

It will not in any way hurt the the alternator, some even replace the alternator fuse with a diode to bump the charge up by 0.5v-1v to help fully top up an AGM battery. Either way they work perfectly fine, and are designed with a drop in upgrade in mind, no need to fear damaging the alternator. That said AGM's are pretty sensitive to over voltage and it will damage them so if your alt is failing and dumping voltage it can degrade them quickly.

 

[eljefino]

The alternator only makes power that the car uses. If an AGM allowed faster recharging after a cold start, it would be "put back in" within 30 seconds at a higher amperage vs a minute at a lower one. Either way the alternator will taper off and make however much power the car needs after that point.

Where you run into problems are things like RVs and sailboats that isolate batteries then slam dead ones, in parallel, onto an alternator not really designed for it, so they run full field for an hour and cook.

 

[Hall]

My wife used to have a '14 Fusion with a flooded battery. Auto-stop-start was an option on all trims except the bottom trim "S" model and if it had auto-stop-start, it came from the factory with an AGM battery. I guess the alternator could have been a different part # on those.... I know the BMS had settings for flooded batteries, AGM batteries, different group sizes, etc. I changed it to AGM and the size I installed and carried on.

 

[D1dad]

I've used them for years, they have been my replacement of choice for anything. In my younger years I was always having problems with batteries and having to ask folks to give me a jump start. Just young and poor so I had to work with what I had and some times that meant a dead battery after I got off work in winter.

That said I now value batteries a lot so I'm far more willing to spend the premium to not have to relive those days. I've used several AGM's and as said my go to of choice. As far as I am aware all modern cars can read the batteries voltage, so they will only charge until a certain point. AGM is a lead acid battery but for simplicities sake traditional batteries have a slightly lower full charge, the alternator will only charge until this point for AGM's though some will charge at a higher voltage 13.2v-13.5v while it is not uncommon for some to charge up to 14.5v

It will not in any way hurt the the alternator, some even replace the alternator fuse with a diode to bump the charge up by 0.5v-1v to help fully top up an AGM battery. Either way they work perfectly fine, and are designed with a drop in upgrade in mind, no need to fear damaging the alternator. That said AGM's are pretty sensitive to over voltage and it will damage them so if your alt is failing and dumping voltage it can degrade them quickly.

I hear you. I was so poor growing up we only got socks at xmas and by the next school year I was embarrassed. Now I’ve got a whole drawer of $20 a pair socks. My wife thinks I’ve got a screw loose because she doesn’t get it. I also remeber push stating my Chevy truck with a 3 on the tree. I replace my batteries just out of warranty.

 

[FoxProTwisty]

Only if the ECM knows the difference in the guts of that battery. But it doesn't so, no.

I used to buy Sears Diehard Plat AGM's as a deep cycle back 25 years ago when I had a big car stereo system and would often listen without the engine running drawing it way down. Even then, it would take about 5-6 years to kill them, far exceeding the 48 month replacement.

AGM's are way more popular today and I've used them interchangeably with SLA's in the same vehicle. They perform no different in the charging system than a SLA other than they have lower internal resistance, discharge quicker in the cold and have a higher float (meaning they like that 14.4v). You can also store a "dead" AGM for years and revive it as compared to a fully sulfated/dead SLA.

 

[willbur]

I've used them for years, they have been my replacement of choice for anything. In my younger years I was always having problems with batteries and having to ask folks to give me a jump start. Just young and poor so I had to work with what I had and some times that meant a dead battery after I got off work in winter.

That said I now value batteries a lot so I'm far more willing to spend the premium to not have to relive those days. I've used several AGM's and as said my go to of choice. As far as I am aware all modern cars can read the batteries voltage, so they will only charge until a certain point. AGM is a lead acid battery but for simplicities sake traditional batteries have a slightly lower full charge, the alternator will only charge until this point for AGM's though some will charge at a higher voltage 13.2v-13.5v while it is not uncommon for some to charge up to 14.5v

It will not in any way hurt the the alternator, some even replace the alternator fuse with a diode to bump the charge up by 0.5v-1v to help fully top up an AGM battery. Either way they work perfectly fine, and are designed with a drop in upgrade in mind, no need to fear damaging the alternator. That said AGM's are pretty sensitive to over voltage and it will damage them so if your alt is failing and dumping voltage it can degrade them quickly.

How does a diode increase voltage? It's just an electrical one way valve. Please explain

 

[pcoxe]

How does a diode increase voltage? It's just an electrical one way valve. Please explain

Silicon diodes generally require 0.6vdc to conduct, so they drop voltage by that amount. Not a significant amount, but still an amount.

 

[D1dad]

My car came with an efb which is in no way an agm and I also don’t have stop start. Honestly wouldn’t buy a car that has it. I saw no reason to use an agm when the car didn’t come with one to begin with.

 

[UncleDave]

It could, but not usually.

One of the bennies of an AGM's is that they have less internal resistance and can be charged faster safely.

What that means is the curve for charging from a deep discharge could look different than a standard lead acid in that it can take more current on its way to full.

Whereas a Lead acid might only take 80% of an alternators output before the curve rolls over - the AGM could take 90-100% of it for a while before rolling over.

Usually what you are doing is recovering from shallow discharges - sitting a week, recover from cranking. In these cases the AGM will be lighter on as its better in terms of self discharge its superior losing less while sitting requiring less output to charge up.

So it's a bit of a trade off in terms of whats harder on an alternator - the occasional longer full blast output, or more frequent longer lower amp outputs.

 

[willbur]

Silicon diodes generally require 0.6vdc to conduct, so they drop voltage by that amount. Not a significant amount, but still an amount.

So you're saying the alternator has to increase output by 0.6 vdc to overcome this drop? But output is already over 12vdc so this drop is not "felt" and no effect on output? But if it drops 0.6, doesn't this decrease output by that amt, not increase? Please explain...

 

[cptbarkey]

My ancient 2003 ram Cummins starts and runs just fine with a single Walmart AGM battery. When it gets around 38 degrees it starts to crank slower but I have no mercy.

 

[pcoxe]

So you're saying the alternator has to increase output by 0.6 vdc to overcome this drop? But output is already over 12vdc so this drop is not "felt" and no effect on output? But if it drops 0.6, doesn't this decrease output by that amt, not increase? Please explain...

Previous writer said he replaced a fuse with a diode to raise voltage. He must have it backwards. Removing a diode from a series circuit should increase voltage, not adding one.

 

[Jetronic]

So you're saying the alternator has to increase output by 0.6 vdc to overcome this drop? But output is already over 12vdc so this drop is not "felt" and no effect on output? But if it drops 0.6, doesn't this decrease output by that amt, not increase? Please explain...

you reduce the voltage to the voltmeter that determines the charge voltage by 0.6Vdc, so the actual charge voltage ends up 0.6Vdc higher.

 

[willbur]

you reduce the voltage to the voltmeter that determines the charge voltage by 0.6Vdc, so the actual charge voltage ends up 0.6Vdc higher.

A unique answer. Voltage is voltage so says the voltmeter . Thankyou- got to think this over a bit

 

[eljefino]

you reduce the voltage to the voltmeter that determines the charge voltage by 0.6Vdc, so the actual charge voltage ends up 0.6Vdc higher.

To enhance this explanation, the engineers are cheap and undersize the big fat wire coming out of the alternator going off to the battery and junction boxes. They know they're going to lose a couple tenths of a volt under high loads, but, hey, copper's expensive.

So they run a second "sensor wire" that goes from, say, the ignition switch, back to the voltage regulator, so the alt can see what the car's "really getting." There'll be a fuse inline, which can be replaced by the diode, which reports back a lower voltage, so the alt works harder to achieve its perceived goal.

 

[willbur]

To enhance this explanation, the engineers are cheap and undersize the big fat wire coming out of the alternator going off to the battery and junction boxes. They know they're going to lose a couple tenths of a volt under high loads, but, hey, copper's expensive.

So they run a second "sensor wire" that goes from, say, the ignition switch, back to the voltage regulator, so the alt can see what the car's "really getting." There'll be a fuse inline, which can be replaced by the diode, which reports back a lower voltage, so the alt works harder to achieve its perceived goal.

Aha! Now I understand.