AGM battery quality vs cost. Do your research.

OllieChristopher

Active member
I am quick to admit I got caught up in some of the marketing and forum buzz in regards to some of the higher end batteries. A few names that are thrown around are Northstar/X2Power, Odyssey, and Lifeline.

The storefronts and reviews are all good and impressive. But the reality is these batteries are no better than some that are half the cost. Lifeline is the best at marketing. They have photoshopped military ships and have great web page. Northstar and Odyssey are more of the same at marketing.

I am of the opinion that almost any cheap AGM battery (with a few exceptions of course) is going to do the job just as well as the ones that are costing double or more in cost.

It is a case of buyer beware. In regards to batteries it's important to point out that you are not always getting what you pay for. I was able to get batteries at 50% less cost with only a few less amp hours and CCA than the "high end ones".

Please do not listen to me but do your own research and you might be surprised to find some outstanding value and quality. It's wise to remember that taking care of your batteries is way more important than just plunking down big money for a brand that has nothing more to offer other than a high price tag.
 

john61ct

Adventurer
No, all this is absolutely false.

True deep cycling capability simply means how many cycles you get drawing down up to 50% DoD

Assuming you regularly get back up to true 100% as per endAmps

and pegging EoL at 70-75% SoH

Those top brands, also adding Firefly Oasis and maybe Full River

will get you double or triple the lifespan of any of the rest, fraudulently labeled as "heavy duty" or "marine" deep cycling.

Sure any old battery will last 3-5 years for a weekend warrior only using say 20-40 cycles per year and willing to keep using past the EoL mark when obvious wear symptoms appear.

If that's all you need, no worries head down to Wally's or AutoZone.

But if your use case is mission critical, and/or you are out there off grid for much of the year, do not want the hassle of replacing in some primitive location

then that approach is penny wise pound foolish.

This Maine Sail article


is actually focused on FLA since they are much better than AGM for this use case

but what he writes is even more true for AGM as well.
 

OllieChristopher

Active member
No, all this is absolutely false.
I will agree to disagree. The top brand AGM's get no more cycles than most any other good name brand AGM of the same size and use. Of course there are inferior and defective products of both cheap and expensive brands. Just because you get a AGM at Walmart or Auto Zone does not make it inferior or go any less cycles than a top brand.

Again you have to research before buying. There is nothing fraudulent calling a AGM battery heavy duty or for marine use. It's what they are made for.
 

Peter_n_Margaret

Adventurer
True deep cycling capability simply means how many cycles you get drawing down up to 50% DoD
The supposed 50% SOC limit to get good life from AGMs is an urban myth and cycles is not a valid method of measuring the life of any battery.
Measure the life of a battery in Ahrs (or Whrs) and you will find that depth of discharge has a relatively small influence. Yes, deeper discharges do result in lower life (including for AGMs, flooded LA and Lithium) but not as much as people seem to believe and there is no "cliff" at 50%, or anywhere else.

It is rare that price is a good indication of quality for any product. Batteries are no different.
Cheers,
Peter
OKA196 motorhome.
 

john61ct

Adventurer
Cycles is the **only** rational measure for deep cycling banks, until calendar lifespan in storage takes over, say for weekenders.

Counting lifespan Ah is so impractical as to be useless.

Yes the 50% guideline is not a magic hard number, but regularly going well below that can cut lifespan to a small fraction, it remains the best rule of thumb for bank sizing

unless you really don't mind replacing it every 2-3 years.

And I definitely am not basing my recommendations on price, many more expensive units are inferior

and at $1/Ah @12V, the Deka FLA last longer and are easier to care for than any AGM, which as I keep saying are poor value

unless you really **need** one of their two advantages, which is rare.
 

john61ct

Adventurer
I will agree to disagree. The top brand AGM's get no more cycles than most any other good name brand AGM of the same size and use.
You obviously have not been exposed to the hundreds of real life cases and dozens of well structured objective tests that prove these statements flat-out wrong.

But I'll let it lie, do as you like if it suits your use cases.
 

Peter_n_Margaret

Adventurer
Cycles is the **only** rational measure for deep cycling banks, until calendar lifespan in storage takes over, say for weekenders.
Only if the cycles are all identical and since that is never the case for RVers (or any application I know), it is a totally useless number.
Yes the 50% guideline is not a magic hard number, but regularly going well below that can cut lifespan to a small fraction, it remains the best rule of thumb for bank sizing
You lost me with "thumbs".
There is a legitimate choice to be made to plan on 30% DOD and equip accordingly.
Just as legitimate is to plan on 60% DOD, install half the battery capacity, have lower emergency back up, spend half the dollars, carry half the weight and replace them a tad more than twice as often.
Cheers,
Peter
OKA196 motorhome
 

Peter_n_Margaret

Adventurer
Fullriver cycles Vs life data attached.
It shows that when EVERY cycle is 50% DOD, the battery lasts 650 cycles. If the battery is 100Ah, that is 650 x 50 = 32,500 Ah total life.
It also shows that when EVERY cycle is 70% DOD, the battery lasts 450 cycles. If the battery is 100Ah, that is 450 x 70 = 31,500 Ah total life.
3% loss of life does not seem to be a significant price to pay for providing an extra 40% of energy per cycle?
Deeper cycles clearly reduce the life of any battery, but nothing like that typically believed.
Cheers,
Peter
OKA196 motorhome
 

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DaveInDenver

Expedition Leader
Fullriver cycles Vs life data attached.
It shows that when EVERY cycle is 50% DOD, the battery lasts 650 cycles. If the battery is 100Ah, that is 650 x 50 = 32,500 Ah total life.
It also shows that when EVERY cycle is 70% DOD, the battery lasts 450 cycles. If the battery is 100Ah, that is 450 x 70 = 31,500 Ah total life.
3% loss of life does not seem to be a significant price to pay for providing an extra 40% of energy per cycle?
That's a convenience question, which is of course one important criteria. There's no universal solution but your chart also says that a DoD of 30% on your 100 A-hr example (assuming 1,450 cycles) would increase your expected life calculation to 43,500 A-hr, around a 35% gain in lifespan.

Which hints to the fact that average depth of discharge and lifespan do not follow a linear relationship. The 50% rule of thumb is a general rule of thumb only because most batteries will have a point at around average 50% DoD where the resulting life cycle expectation will significantly change.

This generalized chart might indicate 60% as a target.

Screen Shot 2021-01-15 at 6.24.37 AM.png

This is Odyssey's, which appears 40% would be better.

Screen Shot 2021-01-15 at 6.34.01 AM.png

So what you're saying that perhaps 50% is just an arbitrary number with no true meaning makes sense. That once you start doing "deep" cycling (which is usually defined as 80% DoD) on a routine basis you're in for a penny, in for a pound. I could see the decision to use your bank fully each cycle rather than carry extra weight you never use. You either stay well on the left side of the knee or you don't.

As an aside, these charts show just how important keeping a battery at 100% SoC. That first 10% of average DoD is a steep drop, persistently leaving your battery at even just 95% SoC is aging it so unnecessarily. In that case a simple float maintainer you plug in every evening is a huge return on investment.
 
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OllieChristopher

Active member
You obviously have not been exposed to the hundreds of real life cases and dozens of well structured objective tests
Real life cases yes I have. Structured tests no. Most consumers who are purchasing these batteries are not doing lab tests. They are just wanting to get the best bang for the buck.

Cycles is the **only** rational measure for deep cycling banks, until calendar lifespan in storage takes over, say for weekenders.
There are so many other variables that have to be taken into account than the cycle count. And yes calendar years is a big one even for a full time user. Then you have heat, vibration, cold, moisture, elevation, etc.

Let's just say you are living off the grid full time and have a set of AGM's that are rated for 2000 life cycles. Those batteries most likely are going to age out way before the cycles are met. There is a remote possibility that they will continue to function after 5 years or more. But then you are looking at other failures beside the cycle count. And sudden failures such as cells shorting out from vibration fatigue can happen to any battery regardless of cost or build quality.

And that was the whole point of this thread. The battery prices have jumped through the ceiling in just the last year due to demand. The market is flooded with a bunch of startup companies that are claiming they are the best. With a little research we can find a good bargain and quality.


Fullriver cycles Vs life data attached.
It shows that when EVERY cycle is 50% DOD, the battery lasts 650 cycles. If the battery is 100Ah, that is 650 x 50 = 32,500 Ah total life.
It also shows that when EVERY cycle is 70% DOD, the battery lasts 450 cycles. If the battery is 100Ah, that is 450 x 70 = 31,500 Ah total life.
3% loss of life does not seem to be a significant price to pay for providing an extra 40% of energy per cycle?
Deeper cycles clearly reduce the life of any battery, but nothing like that typically believed.
I imagine you know more about the abuse batteries are going through than the average "Joe". Seeing you are based in South Australia, and your rig, I'm willing to bet you have been through some of the brutal deserts such as Simpson and others. That is real testing.
 

Rando

Explorer
I would have to second the opinion that the '50% rule' has been completely over stated and over used. There are a lot of folks who seem to think that taking their lead acid battery below 50% will kill it, which is simply not true. Furthermore, this has lead to the marketing mumbo-jumbo that LiFePO4 etc have 'twice the capacity' - they don't, they just have a longer cycle life at every SoC.

The target depth of discharge should be based on your usage scenario, not on some arbitrary number. If you are running an off grid home/boat where you cycle the batteries every day by about the same amount, and maximum lifetime is important - than 50% maybe OK. If you are teleco with a remote mountain repeater, 20% may be the right number.

For most of the folks here that are weekend warriors, only cycling their batteries 10 - 50 times/yer and often with smaller than designed discharges, then 80% DOD still gets you 400 cycles (based on Daves graph), which means you should get 8+ years and calendar aging will get you before cycle aging. Even a 100% DOD (300 cycles) maybe a reasonable depth of discharge for some, and an occasional discharge to 100% is not a big deal. For a vehicle based system, weight and volume are also an important consideration, and this is where the '50% rule' really makes no sense.
 
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Peter_n_Margaret

Adventurer
Good charts, thanks.
There's no universal solution but your chart also says that a DoD of 30% on your 100 A-hr example (assuming 1,450 cycles) would increase your expected life calculation to 43,500 A-hr, around a 35% gain in lifespan.
That is absolutely correct, but there is a price to pay in dollars invested today, weight and space, most of which are in short supply, so it is indeed a choice that we can each make to suit our own circumstances.
That choice can be biased by the presence, or not, of back-up charging capability. No or limited back-up probably means you need more reserve battery capacity. The vast majority of our charging is by solar alone, but we can charge from the alternator direct if required. We don't carry a generator.

Bottom line is that if you need to run the batteries down to zero SOC from time to time, then go ahead, it won't do them any great harm, just get them fully charged again as soon as you can. And if you don't use them at all, they will last for a very long time. :)
Cheers,
Peter
OKA196 motorhome
 

Peter_n_Margaret

Adventurer
I imagine you know more about the abuse batteries are going through than the average "Joe". Seeing you are based in South Australia, and your rig, I'm willing to bet you have been through some of the brutal deserts such as Simpson and others. That is real testing.
As a small aside, We used to use conventional flooded LA for cranking. They typically died (often suddenly) in 2 or 3 years. Then we tried a "garden variety" AGM as a crank. 9 years later I was replacing the 400Ah of house batteries so replaced the crank too, with another ordinary 125Ah AGM.
I concluded that the flooded LAs were physically falling apart internally from the vibrations caused by corrugations. The AGMs have their plates supported in a gel, so were physically much more robust. The crank is chassis mounted, not under the bonnet.
ps... the Simpson is a special place.
Cheers,
Peter
OKA196 motorhome
 

john61ct

Adventurer
There is a legitimate choice to be made to plan on 30% DOD and equip accordingly.
You are absolutely right there.

Most owners think going deeper than 60% is fine, even 80% or dead flat

in fact most have no idea of the curve relationship between Avg DoD% and lifetime cycles.

That 50% guideline is just a useful shorthand "opener" to a topic

which is more complex than most are iterested to explore in detail.

Especially since the chart documenting that relationship is different from every maker that offers such documentation.

My advice (for those motivated to strive fo longevity beyond just a few years) is to only buy from ones that do.
 

john61ct

Adventurer
Are the members here OK with the sobriquet "RVer"?

My understanding has been most are a bit more ambitious than that. . .
 
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