Author Topic: article: Understanding AGM Batteries  (Read 769 times)

Offline Alan Georges

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article: Understanding AGM Batteries
« on: March 18, 2018, 08:09:22 AM »
Over at Off Grid Ham:
http://offgridham.com/2018/03/agm-batteries/
From the article: "AGM batteries are a practical compromise between these two points [flooded lead-acid & lithium]. They’re more expensive than flooded batteries, but nowhere near what lithiums cost."

It's a good take on these batteries and small off-grid power systems, whether for hams or anybody else here.  One more plus of AGM/SLA he doesn't mention is that they come in a bigger selection of medium-to-small sizes than flooded lead-acid batteries.

Offline fratermus

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Re: article: Understanding AGM Batteries
« Reply #1 on: July 07, 2018, 08:13:08 PM »
There is a lot of misinformation in that article.  I'll start with just the above quote from the article.

Quote
Flooded batteries are cheap but come with their own list of disadvantages: They’re really heavy,

Yes, flooded are cheaper in the short and long run vs AGM.  They are cheaper than Li in the short run.  Li should have lower cost over time if the user doesn't smoke them with overtemp conditions, undertemp charging, etc.   

Yes, FLA are heavy, like AGM is heavy.  They are both made of lead.

Quote
produce explosive hydrogen gas,

Yes, like AGM if overcharged.  Both need to be vented.

The difference is flooded is not damaged by overvoltage;  AGM sustains permanent damage.   And folks running consumer grade AGM at the voltages in the article will outgas/kill the AGM quickly.  Example:  here are the Vabs for T-105 flooded and AGM:

FLA - 2.45v/cell (14.7v)
AGM - 2.40v/cell (14.4v)


Quote
need to be replaced more often than most other batteries,

Flat out wrong.  AGM have fewer duty cycles at a given DoD, have less capacity for a given size, and they cost 2X what FLA cost. 


Quote
and require ongoing maintenance that can be a real hassle.

I know.  Watering the batteries 1x/month for <5mins is real beatdown.  To me, the real hassle is ponying up 2x the price for an excellent product hamstrung by being used outside it's designed purpose. If you are offroading you need a jeep, not a corvette.

The only ways AGM are a practical compromise:
  • price, which is silly
  • throughput, assuming the charger can provide the minimum C/5 rate, and preferably C/3.




Offline Smurf Hunter

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Re: article: Understanding AGM Batteries
« Reply #2 on: July 09, 2018, 11:25:16 AM »
I just replaced the battery in the family SUV with an AGM.  Was $15 more.  In theory it will better tolerate kids running accessories without the engine running.

Offline Carl

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Re: article: Understanding AGM Batteries
« Reply #3 on: July 09, 2018, 01:13:19 PM »
  Most generic auto batteries are good for 2 to 4 years in the South...the OPTIMA batteries I have used  (for a bit more money) have lasted 10 to 12 years plus(still works) and I am impressed with the build quality.

Offline fratermus

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Re: article: Understanding AGM Batteries
« Reply #4 on: July 10, 2018, 09:34:16 AM »
In theory it will better tolerate kids running accessories without the engine running.

AGM has better throughput so even when depleted it will be able to crank better than a flooded battery at the same voltage.  And then it should charge faster, too, at least up to the regulation point (commonly 13.8v when the vehicle has been running a while).  Note:  I would not idle the vehicle after a deep depletion b/c the alternator could overheat from lack of airflow.

If you want to be kind to it you could run the accessories off a Low Voltage Disconnect so it never goes below 80-90% or so.  Then charge fully (weekly?) from shore power to get it back to 100% state of charge.