Economical AGM battery

Doomsday Prepper Forums

Help Support Doomsday Prepper Forums:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

DrHenley

Top Poster
Global Moderator
VIP Supporter
Joined
Sep 7, 2013
Messages
17,685
Reaction score
60,089
Location
Columbus, GA USA
First, a quick primer on AGM technology:

AGM stands for Absorbed Glass Mat. There is a mat made of fine woven fiberglass fibers in each cell, and the acid is absorbed (technically adsorbed) in the mat and then wrung out 5% so that it is left at 95%. This is important because it gives the electrolyte some room to expand. Then the glass mats are sandwiched between the plates and compressed and then soldered in place. Because things are tightly compacted, AGM batteries are almost immune to vibration.
Group-AGM-Cutaway-1.jpg

The internal resistance in an AGM battery is much lower than a flooded cell. One benefit of this is that an AGM battery can be charged much faster than a flooded cell battery. It allows a higher discharge rate, which translates into more cold cranking amps in automotive batteries.

Compared to flooded cell batteries, AGM batteries can operate at much lower temperature, are not spill prone (even if case is broken), can be operated in any position, even upside down, and have virtually zero emissions, making them completely safe to use indoors, even in confined spaces. Because they are not spill prone, they can be shipped without HazMat fees, somewhat mitigating the higher cost.

Although there are still deep cycle and non-deep cycle AGM batteries, some AGM automotive batteries (such as the Die Hard Gold) are listed as a deep cycle batteries, yet still have slightly more cold cranking amps than the flooded cell batteries of the same size (775 vs 750 in the case of the Die Hard Gold AGM vs the flooded cell Die Hard Gold of the same size))

And significantly for backup systems, AGM batteries have a much lower self discharge rate than flooded cell batteries, so they can be stored without a float charge much longer without damage. It is still recommended to maintain them with a float charge, but you need a maintainer that has an AGM mode because the voltage at 100% charge is lower than with a flooded cell battery, and overcharging will damage them.

OK end of primer...

I thought I was having battery problems with my car and while looking for a new battery I ran across this at Sears:
http://www.sears.com/diehard-advanc...SellerId=Sears&prdNo=1&blockNo=1&blockType=G1

This is a Die Hard Gold automotive AGM battery, it is also listed as a deep cycle battery. The battery is rated at 75 AH.

Here is the flooded cell Die Hard Gold of the same size:
http://www.sears.com/diehard-gold-automotive-battery-group-size-65-price/p-02850965000P?rrec=true

The price difference is about 20%.

Due to the research I did when looking for batteries for my backup power system at home (6KW Inverter, 2 125 AH VMax AGM batteries), I was familiar with AGM technology. Comparing the cost per AH, this battery (which was on sale for under $120 at the time) was far more economical than any other AGM battery I could find. Even at the current price ($132.74) it is still very economical.

After buying the battery, I discovered my problem wasn't the battery! Fortunately, I had taken an ancient dead battery in for the core charge, so I still had my old battery. I decided to put the original battery back in the car and use the Die Hard in a secondary backup system using a 2 KW pure sine wave inverter for those things that had problems with the modified sine wave of my main inverter (I had been using a conventional flooded cell marine deep cycle battery).

I then went back to Sears and bought another. I told them I was using it for an inverter, so there wasn't a battery that I was replacing, and they graciously waved the core charge!

To get the online price, you have to order online....DUH! Actually the first one I bought was on sale at the store too, but with the second one, I had to use my phone to order the battery (with store pickup), and then wait a few minutes for the order to come through.
 
Last edited:
First, a quick primer on AGM technology:

AGM stands for Absorbed Glass Mat. There is a mat made of fine woven fiberglass fibers in each cell, and the acid is absorbed (technically adsorbed) in the mat and then wrung out 5% so that it is left at 95%. This is important because it gives the electrolyte some room to expand. Then the glass mats are sandwiched between the plates and compressed and then soldered in place. Because things are tightly compacted, AGM batteries are almost immune to vibration.
Group-AGM-Cutaway-1.jpg

The internal resistance in an AGM battery is much lower than a flooded cell. One benefit of this is that an AGM battery can be charged much faster than a flooded cell battery. It allows a higher discharge rate, which translates into more cold cranking amps in automotive batteries.

Compared to flooded cell batteries, AGM batteries can operate at much lower temperature, are not spill prone (even if case is broken), can be operated in any position, even upside down, and have virtually zero emissions, making them completely safe to use indoors, even in confined spaces. Because they are not spill prone, they can be shipped without HazMat fees, somewhat mitigating the higher cost.

Although there are still deep cycle and non-deep cycle AGM batteries, some AGM automotive batteries (such as the Die Hard Gold) are listed as a deep cycle batteries, yet still have slightly more cold cranking amps than the flooded cell batteries of the same size (775 vs 750 in the case of the Die Hard Gold AGM vs the flooded cell Die Hard Gold of the same size))

And significantly for backup systems, AGM batteries have a much lower self discharge rate than flooded cell batteries, so they can be stored without a float charge much longer without damage. It is still recommended to maintain them with a float charge, but you need a maintainer that has an AGM mode because the voltage at 100% charge is lower than with a flooded cell battery, and overcharging will damage them.

OK end of primer...

I thought I was having battery problems with my car and while looking for a new battery I ran across this at Sears:
http://www.sears.com/diehard-advanc...SellerId=Sears&prdNo=1&blockNo=1&blockType=G1

This is a Die Hard Gold automotive AGM battery, it is also listed as a deep cycle battery. The battery is rated at 75 AH.

Here is the flooded cell Die Hard Gold of the same size:
http://www.sears.com/diehard-gold-automotive-battery-group-size-65-price/p-02850965000P?rrec=true

The price difference is about 20%.

Due to the research I did when looking for batteries for my backup power system at home (6KW Inverter, 2 125 AH VMax AGM batteries), I was familiar with AGM technology. Comparing the cost per AH, this battery (which was on sale for under $120 at the time) was far more economical than any other AGM battery I could find. Even at the current price ($132.74) it is still very economical.

After buying the battery, I discovered my problem wasn't the battery! Fortunately, I had taken an ancient dead battery in for the core charge, so I still had my old battery. I decided to put the original battery back in the car and use the Die Hard in a secondary backup system using a 2 KW pure sine wave inverter for those things that had problems with the modified sine wave of my main inverter (I had been using a conventional flooded cell marine deep cycle battery).

I then went back to Sears and bought another. I told them I was using it for an inverter, so there wasn't a battery that I was replacing, and they graciously waved the core charge!

To get the online price, you have to order online....DUH! Actually the first one I bought was on sale at the store too, but with the second one, I had to use my phone to order the battery (with store pickup), and then wait a few minutes for the order to come through.
I hadn't looked into these yet, thanks for the info. I'm planning to start a solar system this coming year and the battery is as important as the collectors.
 
I've been watching the AGM batteries gradually come down in price since I first looked into them. I bought the first one in July 2013, and the second one shortly thereafter when I got my 6KW (12 KW peak) inverter and realized it needed two batteries. I believe the technology has improved since then, and a number of automobiles actually specify AGM batteries now. The Die Hard Gold AGM seems to be a more advanced battery than the VMax. I believe it is what is called a "Dual Stage Performance AGM". Dual Stage AGMs have even lower internal resistance than Single Stage, and can therefore handle 3-4 times as many deep cycles as a Single Stage, and have a higher discharge rate, and can also handle lower temperatures, which is critical for automotive batteries.

Most of the demand for AGM batteries has been due to solar power but it seems that the demand for automotive and power sports AGMs is starting to pick up. They are especially suited for power sports due to the ability to handle vibration and shock. The technology has been around for decades but it was a niche market due to the cost. Older cars may overcharge an AGM battery leading to premature failure unless they are equipped with a voltage limiter.

Another benefit of AGM I failed to mention previously is that they are less prone to sulfation than flooded cell batteries.
 
I've been looking at ni fe batteries. Edison invented them and some are still in service after 80 years. I like having another option here, as ni fe are kind of pricey. I'll do a lot more reading as I get closer to actually put a system in use next year. I don't care to get completely off grid, but would like to know life will be less affected by a grid down situation.
 
I've been watching the AGM batteries gradually come down in price since I first looked into them. I bought the first one in July 2013, and the second one shortly thereafter when I got my 6KW (12 KW peak) inverter and realized it needed two batteries. I believe the technology has improved since then, and a number of automobiles actually specify AGM batteries now. The Die Hard Gold AGM seems to be a more advanced battery than the VMax. I believe it is what is called a "Dual Stage Performance AGM". Dual Stage AGMs have even lower internal resistance than Single Stage, and can therefore handle 3-4 times as many deep cycles as a Single Stage, and have a higher discharge rate, and can also handle lower temperatures, which is critical for automotive batteries.

Most of the demand for AGM batteries has been due to solar power but it seems that the demand for automotive and power sports AGMs is starting to pick up. They are especially suited for power sports due to the ability to handle vibration and shock. The technology has been around for decades but it was a niche market due to the cost. Older cars may overcharge an AGM battery leading to premature failure unless they are equipped with a voltage limiter.

Another benefit of AGM I failed to mention previously is that they are less prone to sulfation than flooded cell batteries.
When I start building my solar electric system this spring I'll be using AGM's in my battery bank. Another advantage of AGM's is they can handle cold temperatures better. Meaning they can be installed in an unheated location. AGM'S can also be installed at any angle if necessary.
 
If lithium ion batteries ever come down in price that will be the way to go...unless they come up with something better. The For now, it looks like the advanced AGMs have the best combination of features and price. I think the more advanced Dual Stage AGMs have not been on the market long enough to gauge their long term economy, but based on what I have read, they should have a pretty decent life expectancy.

The nickel-iron batteries are good, but the startup cost is very expensive. Because of the long service life, they probably will be the best battery for extended SHTF situations...if you can afford them...

I've done a few rough calculations of cost per AH for various batteries at current price. This is only the purchase cost, not the long term cost which I don't have enough info to calculate.

Generic Sealed Flooded Cell Deep Cycle 100AH: $1.74/Ah
Die Hard Gold AGM 75AH: $1.77/AH
VMax Solar AGM 125AH: $2.08/AH
Generic Lithium Ion 100AH: $6.25/AH
Generic Lithium Iron Phosphate 200AH: $7.35/Ah
Encell Nickel Iron 100AH: $12.45/AH
 
Great info, Doc. I didn't realize that AGM's were available in automotive style batteries yet. Wish I'd known...I just bought a regular (flooded) deep-cycle a couple of weeks ago. An Interstate, which is a good brand, but it's not an AGM.
 
If lithium ion batteries ever come down in price that will be the way to go...unless they come up with something better. The For now, it looks like the advanced AGMs have the best combination of features and price. I think the more advanced Dual Stage AGMs have not been on the market long enough to gauge their long term economy, but based on what I have read, they should have a pretty decent life expectancy.

The nickel-iron batteries are good, but the startup cost is very expensive. Because of the long service life, they probably will be the best battery for extended SHTF situations...if you can afford them...

I've done a few rough calculations of cost per AH for various batteries at current price. This is only the purchase cost, not the long term cost which I don't have enough info to calculate.

Generic Sealed Flooded Cell Deep Cycle 100AH: $1.74/Ah
Die Hard Gold AGM 75AH: $1.77/AH
VMax Solar AGM 125AH: $2.08/AH
Generic Lithium Ion 100AH: $6.25/AH
Generic Lithium Iron Phosphate 200AH: $7.35/Ah
Encell Nickel Iron 100AH: $12.45/AH
I knew nickel iron was more up front, but that's a lot more! I'll do some research on it. I read somewhere there was a patent on hem that expired, so maybe some competition could bring down the price. The longevity was what caught my interest. Unfortunately dollar signs do as well.
 

Latest posts

Back
Top