Any redeeming qualities of AGM batteries?

[Riley5781]

You guys have taught me well. I have a well sized 48V system with 3.6KW of panels feeding my FLA battery bank of S-550 Rolls batteries.
I measure the SG every other day using temp compensated hydrometer and working to keep the absorb time optimized.

My summer vacation home is in an area where everybody on the lake shore is off-grid. My friend and neighbor has a much smaller 12V system that is only used for LED lighting and TV once and awhile. He swears by AGM batteries and thinks I am crazy to use FLA. I answer with you can't even measure the SOC with AGM but that doesn't seem to matter to him.

My question: Is there any redeeming qualities about AGM besides you don't need to monitor water levels and replace water once and awhile?

Is it fair to say that if you are going to ignore your battieries that AGM is better?

I am just trying to understand if there's any real value to the additional cost of AGM.

Thanks guys.

[Mike90250]

1) they cost more, so you help support city hall with the increased tax revenue
2) they don't last as long as FLA, so you can support city hall again, sooner.

[SunEagle]

Two things that are better about AGM batteries;
1. They can be stored on their side and will not leak.
2. They can accept a faster charge rate then FLA type

Having said the good things above I agree with Mike that they are much more expensive and probably not worth the cost since they will not provide the same number of cycles that an FLA bank can provide.

[littleharbor]

1. They allow installation in tight enclosed areas without having to worry about excess hydrogen gas build up which is detrimental to electronics.
2. In my case I have my battery bank stacked 4 across x 2 high under a workbench. If I had to check electrolyte levels and SG this configuration wouldn't be possible.
3. They can be charged with twice the current of FLA batteries allowing a larger array and other charging sources and having better odds of reaching full charge on less than perfect solar days.
4. In seasonal, vacation homes, with their low self discharge, you can disconnect all loads and charging sources and leave them for a full season without having to worry about self discharge like you would with FLA batteries.
5. They make for very clean long term installations without having to worry about acid mist building up on the top of the batteries and fouling your cables.

Yes they're more expensive. Yes, they don't last as long as a well maintained FLA battery bank.

OTOH negligence will ruin a good set of FLA batteries in short order. where there is little maintenance with AGM batteries. They have critical charging voltage limitations, but this is simply a matter of setting charging parameters correctly when you install the batteries.

[J.P.M.]

1. They allow installation in tight enclosed areas without having to worry about excess hydrogen gas build up which is detrimental to electronics.
2. In my case I have my battery bank stacked 4 across x 2 high under a workbench. If I had to check electrolyte levels and SG this configuration wouldn't be possible.
3. They can be charged with twice the current of FLA batteries allowing a larger array and other charging sources and having better odds of reaching full charge on less than perfect solar days.
4. In seasonal, vacation homes, with their low self discharge, you can disconnect all loads and charging sources and leave them for a full season without having to worry about self discharge like you would with FLA batteries.
5. They make for very clean long term installations without having to worry about acid mist building up on the top of the batteries and fouling your cables.

Yes they're more expensive. Yes, they don't last as long as a well maintained FLA battery bank.

OTOH negligence will ruin a good set of FLA batteries in short order. where there is little maintenance with AGM batteries. They have critical charging voltage limitations, but this is simply a matter of setting charging parameters correctly when you install the batteries.

So, because one battery has different +'s / -'s from the other(s), not every battery will be as fit for purpose, depending on the application and duty requirements. Education is the key.

But I bet, because most folks don't take the time or make the effort to learn and, because most everyone is afflicted with the low first cost syndrome, they will go with the low initial cost every time regardless of suitability to the application and then go through some pretty bizarre mental contortions to justify what's usually an ill informed choice.

[PNjunction]

I'm actually PRO-agm, but ONLY when engineered properly. In other words, there's a big BUT waiting ...

The fact that you can push 0.25 to 0.3C into them is a benefit for solar, where charge time is limited usually, especially during winter or harsh climates. More advanced "pure lead" types can have up to 1C or more charge acceptances - which means you can use big arrays to get the job done quickly.

Higher voltage under load - the lower resistance of agm's, especially the pure-leads, means that your inverters and whatnot are operating more efficiently.

BUT - you will NEVER properly charge an AGM in one single solar day!! Thus, you are always "walking them down" every day in capacity. Maybe not visible at first, but it happens. No matter how fast you charge them, they MUST have at least 8 hours or more of float. Not going to happen on this planet in a single usable solar day. And nobody in their right mind would run a genny for 8 or more hours floating wasting fuel.

This is the biggest reason for disappointment compared to flooded, even with it's lower charge acceptance rate. Users don't know how critical that last one-percent is.

Things change if one is not in a daily-cyclic routine however! If you can afford to "waste" a day solely left to recharge that critical last "one percent" properly, you can maintain an agm quite well.

Your rv buddy is only using an agm very lightly. It is quite reasonable to think that with very light use, he's treating the agm "ok". Not perfectly, but time vs cycle life may be hard to determine with his load. He might be killing it softly with his song.

In the end, if one is doing daily cyclic deep discharges with agm, you KNOW you are walking it down, but every week or so, you need to waste a lot of available panel energy floating it back into shape. As long as one knows and is ok with that, then fine.

This is one reason why agm users who are doing daily cyclic duty, should NEVER float, but stay in absorb until the sun goes down. That is, if your absorb is set for say 14.6v, then your float voltage should also be 14.6v. Non-daily cycles and plenty of sun? - different story - drop the float to manufacturer's recommendations.

[jflorey2]

1. They allow installation in tight enclosed areas without having to worry about excess hydrogen gas build up which is detrimental to electronics.

Acid is detrimental to electronics. Hydrogen, in the quantities that batteries produce them, is not. (It is, however, an explosion hazard.)

OTOH negligence will ruin a good set of FLA batteries in short order. where there is little maintenance with AGM batteries.

Negligence will ruin AGM batteries as fast - often faster - than FLA batteries, since you cannot replenish electrolyte.

[Mike90250]

1. They allow installation in tight enclosed areas without having to worry about excess hydrogen gas build up which is detrimental to electronics......

False. In case of overcharging, battery failure or catalyst failure, they WILL produce hydrogen and oxygen gas and you MUST provide the same venting provision as for flooded batteries.

The only upside, is lack of acid mist vapors for 98% of the battery life. When the battery begins to fail, you get expelled acid mist, hydrogen and oxygen. Only the acid mist is detrimental to most things (including paint, metal finish and electronic gear)