quote:

Originally posted by Milliron:
Word of caution. How old is your wife's car? The reason I ask is that some years ago I replaced the battery in my truck with an AGM battery (newer, better right?)

Everything was fine until it died while transporting a whole truckload of Boy Scouts on the way back from camp. Jumped it, kept dying. Drove it to the mechanic.

Come to find out the alternator in my 2011 Tundra doesn't generate enough voltage to adequately charge the AGM battery, which is why it kept dying. Replaced the battery with a standard battery and problemo solved. That was a $300 lesson.

The charging and float voltages on lead acid and agm are so close that it's negligable and that didn't kill your alternator.

It didn’t kill the alternator. It just didn’t charge completely.

I bought an AGM from Costco. Two months later it went dead. They gave me a new one. Car is a 2018 Accord.
Lesson? If you're going to buy an AGM, buy it from Costco.

quote:

Originally posted by HRK:
Interesting tidbit Walmart sells an AGM battery, and I'd suspect it's a Duracell battery in Walmart cloths, they look exactly the same and it's $20 less for the same Group 48 model.

There are only 2 or 3 major battery manufactures for the US market, brands are just stickers and the sticker doesn't tell you anything about the manufacturer.

Depending on the region you live in, Duracell from Sam's and EverStart from Walmart are the same battery. However, Walmart has two versions of their batteries. The cheaper one differs internally with plate count and even the lead alloy may differ too.

The list of batteries supplied by one manufacturer to different customers is long and ever changing. There are battery companies outside of the US that are sold here too. Do not be afraid of those batteries either. Some are made just as well, if not better, than the ones made here.

quote:

Originally posted by DoctorSolo:
I think Milliron's alternator is jank. AGM's don't like to be charged/discharged at high rates the way a lead-acid can tolerate, but 21st century cars will not see a difference in normal use.

Toyota wouldn't F that up IMO.

I hear "mechanics" say outlandish things all the time. All the time.

ALL THE TIME.

From the engineering side, Toyota has under-driven their alternators for years to get that 0.0001% increase in gas mileage. They sit just above 'not charging' at idle. You get a batch of mediocre alternators & it's slightly under that - I've dealt with that in Tundra & Sienna in more than N=1 sample size. Add in short trips of stop & go driving, older batteries and internet complaints and you get goofy ideas about AGM vs normal lead acid & charging voltage.

I suspect the models that can be programed have software looking to 'unload' the alternator for the same reasons - gas mileage. A solution in search of a problem.

I sold batteries in college (sears). I saw a lot of early deaths & some that lasted 15 years. I learned a little about the industry.
I worked in automotive electrical systems for 18 years. Not with batteries or alternators, but I connected them together. I learned a lot more about the industry.
My opinion on batteries is the same as my opinion on brand of oil or gasoline - it doesn't really matter in the long run.
I do prefer AGM over wet plates, but in a daily driver, it doesn't really matter for performance or longevity. If the battery is interior, definitely AGM just for less chance of acid spilling.

quote:

Originally posted by snidera:

quote:

Originally posted by DoctorSolo:
I think Milliron's alternator is jank. AGM's don't like to be charged/discharged at high rates the way a lead-acid can tolerate, but 21st century cars will not see a difference in normal use.

Toyota wouldn't F that up IMO.

I hear "mechanics" say outlandish things all the time. All the time.

ALL THE TIME.

From the engineering side, Toyota has under-driven their alternators for years to get that 0.0001% increase in gas mileage. They sit just above 'not charging' at idle. You get a batch of mediocre alternators & it's slightly under that - I've dealt with that in Tundra & Sienna in more than N=1 sample size. Add in short trips of stop & go driving, older batteries and internet complaints and you get goofy ideas about AGM vs normal lead acid & charging voltage.

I suspect the models that can be programed have software looking to 'unload' the alternator for the same reasons - gas mileage. A solution in search of a problem.

I sold batteries in college (sears). I saw a lot of early deaths & some that lasted 15 years. I learned a little about the industry.
I worked in automotive electrical systems for 18 years. Not with batteries or alternators, but I connected them together. I learned a lot more about the industry.
My opinion on batteries is the same as my opinion on brand of oil or gasoline - it doesn't really matter in the long run.
I do prefer AGM over wet plates, but in a daily driver, it doesn't really matter for performance or longevity. If the battery is interior, definitely AGM just for less chance of acid spilling.

The guy I talked to said AGMs were primarily pushed by BMW because they moved the battery into the trunk for weight distribution, hence the desire for a non-lead acid battery. Don’t know how true that is, but it made sense.

AGM, absorbed glass mat, is still a lead acid battery; the same chemistry as a non-AGM lead acid battery. The difference is in the construction with the AGM battery having absorbed glass mat placed between the lead plates.

The material acts as a sponge soaking up the same sulfuric acid and distilled water a non-AGM battery uses. The mat helps support the plates and withstand vibration. Expansion and contraction due to heating and cooling puts extra stress on those plates. Overcharging an AGM battery will do the same thing. The acid starts to boil and there’s no room for the pressure to go. The bubbles stay within the mat causing the mat to expand and the entire battery to expand. I’ve cracked the cases of two AGM batteries doing this with supposedly automatic chargers complete with AGM settings.

There’s an air pocket between the acid and top of a non-AGM battery that compresses to compensate for this.

On my vehicles in Florida that aren’t garage kept, the AGM batteries last 3 years, but with the 4 years replacement warranty, I get new ones. Batteries under the hood heat to 140 during the day and cool off to 75 at night. The mat expands differently than the lead plates putting pressure on the lead plates. Again, this doesn’t happen with a non-AGM battery because any expansion of the liquid that happens heating it to 140 is counteracted by the compression of the air built into the battery.

That’s my completely uneducated guess anyway based on currently maintaining 31 or so batteries in batteries in various vehicles.

quote:

Originally posted by Milliron:

The guy I talked to said AGMs were primarily pushed by BMW because they moved the battery into the trunk for weight distribution, hence the desire for a non-lead acid battery. Don’t know how true that is, but it made sense.

Traditional wet-cell batteries release gas when charging, not good in an enclosed environment. Inside a cars weather sealed area, AGM or SLA only. Trunk may or may not qualify, but I would replace with SLA/AGM if I was buying (and it was readily available).

I've come up with some goofy explanations of why BMW does goofy things the way they do them, but weight distribution is probably down on the list, I'd suspect. Sounds like the type of thing you add to the list when you are trying to justify the cost of a change you want to make.... From my perspective, the cost of the battery cable increase from moving the battery to the trunk would be hard to overcome, so you'd have a ton of 'positives' on the list - like 'better weight distribution, car go more faster'