Flooded lead acid usage compared to AGM

[Plant]

What rate of discharged is considered okay for flooded batteries?  I've been doing my planning calculations with AGM in mind, understanding that they should not be drained further than %50, and thus battery Ah need to be calculated with that in mind.  Can traditional flooded batteries drain further? The book I have does not even seem to acknowledge flooded as an option so I want to make sure my calculations are right.

Mod edit, AGM = Absorbed Glass Matt

 

[John61CT]

No, the relative life cycles lost vs avg DoD curves are similar for all chemistries.

AGM will support higher **voltage** when discharge current is very high, say large inverter load like a microwave for short periods, FLA needs a bigger bank.

FLA generally last longer, more forgiving of less precise care regimes, easier & more robust, and of course, lots cheaper.

In the US market, the best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH pair from BatteriesPlus or Sam's Club. Deka labeled same batts also sold at Lowes.

Mod edit, FLA = Flooded Lead Acid, DoD Depth of Discharge. come on John

 

[bluegoatwoods]

I'm afraid I don't know the answer. But I'm going to hope that a flooded battery can take a higher discharge than a gel or a glass mat. It's because I chose flooded batteries. Just bought them the other day, as a matter of fact.

I actually wouldn't have even blundered into your thread, not knowing what I'm talking about, if it weren't that I figure I might as well mention the reasons I chose flooded. As sort of a side topic.

When choosing the flooded batteries the decision that they must never be in a human occupied space was automatic, of course. But I didn't feel any loss since I wouldn't feel good about having gels or glass mats in our living space either. And with flooded batteries I'm going to need to keep distilled water levels up and measure specific gravity regularly. But that's okay since it seems like a good idea to be practiced at that.

I'm hoping that flooded batts will give better bang-for-the-buck as long as I'm good about maintaining them.

 

[Trebor English]

The lead / sulfuric acid chemistry is the same.  The effect of lead sulfate is the same.  The difference is that with a flooded battery overcharging to convert buried lead sulfate resulting in water loss due to electrolysis can be corrected by adding water.   

 Overcharging AGM batteries resulting in electrolysis is supposed to not matter as the hydrogen and oxygen are supposed to recombine.  In theory.  

The depth of the discharge is important.  The amount of time the battery is left discharged matters.  Partial recharging followed by a new discharge cycle matters.  An 80% discharge followed by a prompt 100% recharge is less harmful than 30% to 50% discharge followed by recharge only to 95% full.  Repeated undercharging is the most baddest thing.  

Flooded batteries tolerate gassing if water is added as necessary.  Gel batteries are ruined when bubbles form as they are permanent.  Charging too fast should be avoided.  

For a first battery, a learning battery, I recommend flooded.  They are cheaper and more robust than AGM or gel.

 

[Almost There]

  Can traditional flooded batteries drain further?

50% discharge is maximum for long life for Flooded Lead Acid batteries (FLA),

The only advantage of AGM (Absorbent Glass Mat) is that they don't have to be placed in an upright position

The 'FLA can't be used in a human environment' theory is up for much discussion. Lots of us use them in our vans without putting them in a sealed battery case that is vented to the outside with no problems. I sleep with 4 6V FLA batteries right  under my head and have never smelled them. Course they aren't being bulk charged while I'm sleeping but even during the day time I don't smell them. Others are super sensitive to the smell or have good imaginations...  

The other difference is in the care of feeding of them. Sealed batteries cannot be topped up, FLAs can and should be checked regularly and topped up with distilled water to replace what is lost.

AFAIK the only batteries that will withstand a deeper depth of discharge (DOD) is lithium which can go to 80% IIRC.

 

[Plant]

Thank you guys for the info, very helpful.

Initially I was determined to get AGMs but after doing my usage calculations, I frankly could not stomach the cost for 4 - 200Ah AGMs. I got pulled toward FLA batteries primarily due to cost. Maintenance does not bother me, locating them in my living quarters does. So, I'll be building a custom enclosure, sealed to my interior, vented to the exterior.

Regarding batteries. I've seen some good words for Trojan or Superior T-105s. I think I can get them for a good deal locally. How do they compare to Deka/East Penn batteries?

 

[Almost There]

I've been running with 4 Trojan T105 REs for almost 3 years now and I'm completely happy with them.

If you can get the T105RE's rather than the T105s I'd say go for it. They're 7 lbs heavier and slightly taller but rated for, IIRC, 5000 discharge cycles as compared to something like 1800 for the 105s.

I had dealers try to bad mouth them but as far as I could see it was because they had whole skids of the T105s on hand and didn't want to have to order the REs. I ended up driving from Quartzite to Phoenix to pick mine up.

 

[Plant]

Hey thanks, Almost There! A quick search and I see they well under $200 for the T105REs. They are definitely on my short list. I'll find out what is available locally and go from there. Driving does not bother me either to save some money.

 

[squire]

I suggest not buying batteries before you need them. Batteries have a "life" and why waste months of it. My first set of 4 T105's lasted 5 yrs and I am not proud of how I treated them.

 

[squire]

Just a thought, in the planning and building stage build some cardboard boxes the size of your batteries (and other know pieces), sure beats lifting heavy objects and you will get the "scale" needed.

 

[John61CT]

There is **nothing** magic about 50%.

Look at the DoD vs cycle chart for your model.

Go "too deep" say 70% DoD too often, they need replacing sooner, maybe even one season.

Stick to only 20% discharge might last ten years.

Other care factors involved as well in longevity of course.

 

[Plant]

Good point about holding off on the purchase. I can do that. My primary need at this point is dimensions and quantity so that I can build the box, and know minimum cabinet size to accommodate. I'll be looking at the Duracell that John suggests, and the T105s and see if I can come up with something that can accommodate various choices.

 

[Almost There]

If you're going to be building the battery area in to a cabinet that is going to make it difficult to service the batteries then it might make sense to add a  watering system for them.

I don't know if all companies offer them but Trojan makes a watering system that replaces the caps, adds water lines  and a hand pump. To activate you simply insert the pump end in to a jug of distilled water and pump. The system then fills all cells to the proper depth making it easy to keep the batteries properly filled.

I've lived for 3 years having to pull the batteries from an awkward place under the bed to check and fill them. I'm treating myself to a watering system for Xmas - should have done it in the first place.

 

[Plant]

I'll make sure I have clear top access. Possibly a slide out counter top over the solar area.

 

[John61CT]

T-105s may be a little better than the Deka, but I wouldn't pay more than 10-20% more, adjust per-AH of course

Delivery / pickup distance and return policies of the seller are of course relevant too.

Crown, Superior & US Battery also good, Rolls / Surrette the best, just talking FLA that is.

 

[frater secessus]

There is **nothing** magic about 50%.

Look at the DoD vs cycle chart for your model.

Agreed. 

50% DoD is a widely-repeated compromise between usable capacity and bank longevity.  Cheapest Ah/$ is theoretically found at something like 20% DoD but would require lugging around 2.5x more lead.

 

[John61CT]

you also can't take the DoD vs cycles chart as real

even with the most honest vendor, they are **lab** tests not IRL

 

[Spaceman Spiff]

but lab life cycles are the best you can expect.

 

[squire]

I'll make sure I have clear top access.  Possibly a slide out counter top over the solar area.

I made the mistake of making my battery box with not enough air space around my 4 T105s. My thought was to keep them warm in the winter but they go too hot in a week of over 100 degree days. The water got low ( I always checked them on the 1st of the month and little water was ever needed) that month and damaged them.

 

[John61CT]

but lab life cycles are the best you can expect.

With lead batts far more than you'll actually get.

My point is the cycle-lifetime destruction resulting from deeper discharging is grossly underestimated by the graph.

So IRL not just shifting the curve over, but radically changing the slope / shape.