AGM Battery Life

[JHZR2]

AGM has never been a panacea despite some thinking they were. They still fail, still sulfate, etc. They have less electrolyte. The only real benefit structurally is that they cant slosh off as much lose material from the plates since the glass mat will hold material at the plates theoreticslly. They don’t self discharge as fast, and don’t gas which is great in some cases, but car draws still damage them.

 

[barryh]

I have to wonder why some automakers purposely under charge AGM batteries.

All modern cars with smart alternators are deliberately undercharging the battery and it's not just an AGM thing. They use a complex algorithm to set the charging voltage, In simple terms as long as the battery is 80% charged they aim to charge at full voltage only on the overrun because that's free energy and then drop the voltage down to a lower voltage under acceleration. They do it for the marginal benefit it gives to headline fuel economy and emission figures.

My experience is the net result is something less than a fully charged battery at the end of every tip. Driving for a couple of hours tends to get the battery nearer to full charge but shorter trips leave the battery needing a couple of hours on a charger.

This is so universal these days that perhaps the battery manufacturers have changed the chemistry to make batteries more tolerant of being under charged, that's if such a thing is possible.

 

[930.engineering]

My diesel BMW came with an AGM battery that was still going strong at 8 years. I changed it as a preventive maintenance matter because I don't like changing batteries in sub zero weather.

My 2013 Mini has its first AGM (2012 data code). After 11 years it's still alive,
knock on wood....
.

 

[f355spider]

AGM batteries when installed at the factory usually have vehicle electrical systems optimized for AGMs. If you install an AGM in a car designed for a flooded acid battery, it likely will not last as long. My diesel BMW came with an AGM battery that was still going strong at 8 years. I changed it as a preventive maintenance matter because I don't like changing batteries in sub zero weather.

My experience does not show this. I have an AGM battery for 4+ years in a daily driven 2001 E39 540 BMW. It still tests better than its rating. Yet I went through two East Penn flooded batteries in about four years that simply no longer held a charge.

Consumer Report has previously recommended AGM batteries for cars that did not come with them, as they notice as a group, AGMs tend to perform better and last longer. (not always of course, there are still very good flooded batteries out there)

 

[f355spider]

AGM has never been a panacea despite some thinking they were. They still fail, still sulfate, etc. They have less electrolyte. The only real benefit structurally is that they cant slosh off as much lose material from the plates since the glass mat will hold material at the plates theoreticslly. They don’t self discharge as fast, and don’t gas which is great in some cases, but car draws still damage them.

THIS! Also the OPs 90 yo mother is probably not daily driving, which leaves the battery in a less than ideal state of charge. And in his own case, newer cars have high draws....he's clearly driving a lot, but heat also takes it toll. And as we all see from this forum, batteries can be fickle devices and seem to still have a higher than average failure rate...just because.

As a group, I have had better luck with AGM, but have still had a few bad ones, like Optima red tops...three in a row leaked. No longer use those. I have also had a few excellently performing flooded batteries too.

 

[Propflux01]

THIS! Also the OPs 90 yo mother is probably not daily driving, which leaves the battery in a less than ideal state of charge. And in his own case, newer cars have high draws....he's clearly driving a lot, but heat also takes it toll. And as we all see from this forum, batteries can be fickle devices and seem to still have a higher than average failure rate...just because.

As a group, I have had better luck with AGM, but have still had a few bad ones, like Optima red tops...three in a row leaked. No longer use those. I have also had a few excellently performing flooded batteries too.

She drives to the grocery once or twice a week, then once a week drives 40 miles one way to another town for appointments. So not too terribly much. Me, I drive 25+k a year, work and monthly trips to KCMO. was just odd that in two different styles if driving, both batteries took a dump about the same time, and in the same manor.

 

[Tundragod]

My 6/9/2012 Die Hard AGM battery in my 08 Accord daily drive is still going like the drumming rabbit.....

 

[nthach]

I’ve had an Optima fail in less than 3 years, but I’ve had a Deka make it beyond warranty, it died 5.5 years. Both were used in a car with constant power draws(smart key, EVAP monitoring, JBL amp that doesn’t “shut off” but is in sleep mode.

The Toyota hybrids use a DC-DC converter which in itself is a small DC-AC inverter which then inverts back to DC. It seems to apply a constant voltage and current to the battery.

 

[f355spider]

I’ve had an Optima fail in less than 3 years, but I’ve had a Deka make it beyond warranty, it died 5.5 years. Both were used in a car with constant power draws(smart key, EVAP monitoring, JBL amp that doesn’t “shut off” but is in sleep mode.

The Toyota hybrids use a DC-DC converter which in itself is a small DC-AC inverter which then inverts back to DC. It seems to apply a constant voltage and current to the battery.

I've had three Optima red tops fail in less than 3 years each, due to leaking (size 34R). They still load tested fine and exceeding their CCA rating. They used to be great, I had good luck with them 20 years ago. But in the past decade their QC stinks.

 

[ARB1977]

Had a die hard platinum in my beloved 2002 Tacoma 3.4L that going strong for 7 years upon trade in. In my 15 I had a Duracell AGM that lasted 5 years. Replaced it just recently with a die hard platinum.

 

[Thermo1223]

I put a AGM in the Colorado from Wallyworld back in 2020. Still had the factory GM battery from 2015 that was starting to get weak. No issues thus far and I do put in on the charger before winter just because. I am unsure if GM's algorithm will adjust for it being an AGM. I do know on cold mornings it is pumping 15v into it most of the way to work. It also will with headlights or other high loads never drop the voltage below 13.8.

That doesn't account for the scenarios where it will varying from 12.3 to 13.2 if no loads are present but it takes it being temperate outside and/or highway driving to get that.