AGM or GEL Batteries? Which is best?

[SageOldmann]

I have been putting this off for a long time due to cost, but I was just about to buy some new AGM batteries when I saw a post somewhere that said AGM are not true deep cycle batteries that are not good for solar use. Is that true? I found that interesting as I followed a discussion involving two preppers. They both have set up their systems to be able to run a kitchen refrigerator in a power failure, or so they claim. They both use mppt controllers. They both say their compressors draws about 7 amps during start. One uses AGM and the other GEL batteries. The AGM guy claims his batteries provide better initial surge power when starting and are trouble free. His bank is 270ah with four 100 watt panels and a 1,000 watt inverter. The GEL guy claim his batteries are true deep cycle batteries with thicker plates that can provide double the cycles (1200 verse 500 for AGM) and are better for daily use. He has a 300ah bank to give extra power for the starting surge, and five 100 watt panels, don't remember what size inverter but I think it was 1500 watt. If I wanted to be able to run my refrigerator during a power failure, which happens several times per year for 36 to 48 hours, which of these two would be better for me to use, the AGM or the GEL system, and why? (I use a generator now when power goes out, which is getting very old). Is a 1000 watt inverter really enough to start a compressor? I have my doubts. I have limited funds but have enough to bring my current system up to either of these levels. (Lithium is out of the question due to cost.)

[Sunking]

Never ever use Gel, and AGM is a niche application. Best bet is always flooded.

AGM and FLA both come in deep cycle versions. However AGM cost is about 100% higher and only about half the cycle life of FLA batteries. AGM has its place in solar, but you really need to justify the cost. AGM has two advantages you are paying up for.

They have extremely low internal resistance which means they can handle larger C Loads of up to 15 minute discharge times which is real important if it is a rocket motor pumping the fuel in the expansion chamber, or attic cold where temps dip to -40 degrees.

So is this for a rocket motor or snow mobile? Or perhaps an aircraft where spills cannot be tolerated. If not your best bet is Flooded Lead Acid, half the cost up front and last twice as long. and longer than lithium. Pay your money, take your chances.At the end of battery life, AGM wil be about 400% higher than FLA.

Leave the gel cells for morons. Gel cells are for alarm panels and egress lighting using a Float Charger.

So with all that said use Gel battery Charlie Brown.

[SageOldmann]

Can't use flooded. Batteries are in a confined space with open flame water heater. No other option. But you have answered my question Linus. In your opinion, No GEL. The Guy with the AGM is actually more on target given the big load from the compressor start up based on what you said. Anyone else care to weigh in?

[SunEagle]

Can't use flooded. Batteries are in a confined space with open flame water heater. No other option. But you have answered my question Linus. In your opinion, No GEL. The Guy with the AGM is actually more on target given the big load from the compressor start up based on what you said. Anyone else care to weigh in?

AGM ,while expensive compared to FLA type, are useful in enclosed areas. GEL are just about useless as a deep cell with high cycle rate.

The AGM are probably your best choice unless you want to play with one of the Li chemistry type but that brings on a whole new set of rules to keep them charged and happy. They may also be much more expensive then the AGM depending on what you get.

[SageOldmann]

Ok SunEagle you seem to agree with Sunking about the GEL batteries. I've seen other posts from you around this forum and you seem pretty sharp with a lot of experience so I'll 86 the the GEL idea and focus on the AGM. So do you think if I duplicate the 270ah battery bank with four 100 watt panels and a 1,000 watt pure sine wave inverter that I'll be able to run the refrigerator like that guy says he does, or should I upgrade everything a bit like the other guy?

[Mike90250]

Gel is useful for emergency exit lights, that only get used 1 every 4 years. They do not recharge quickly and would be a bad choice.

AGM is available in true deep cycle construction.

AGM, at end of life, or in an overcharge condition, begin to vent (they have emergency 3psi vents) the same gasses and fumes as flooded, so their container still needs explosion proof venting.

My suggestion, use the expensive, short lived AGM, and in 2 or 3 years, when they fail, there may be some realistic plug-play Lithium batteries to use instead.

Also, consider building the bank out of two series wired golf cart batteries (6v, 200ah) which solves the AGM "battery in parallel" problem.
(AGM is so low resistance, that the parallel interconnect wires will steer power to one battery which will end up doing 80% of the work and fail earlier than expected)

https://www.samsclub.com/p/duracell-agm-golf-car-battery-group-size-gc2agm/prod3870119

[SageOldmann]

That was very helpful Mike 90250. GEL is definitely out now. Do you know any brands that are TRUE deep cycle AGM if I stick with 12 volt? I can't tell one from another. I Iike your 3 year game plan. Lithium has to come down in price by then. Would the golf cart batteries give me 12 volt, 400 AH if I wire in series with just 2 batteries? The Duracell AGM Golf Car Battery at Sams are out of stock. Any other suggestions for an AGM version?

[Mike90250]

No, just 2 GC2 batteries would only give 12V 200ah If you need close to 400ah, you would have to get Floor Scrubber AGM batteries,

Big batteries = big price expect about $500 each, 6v 370ah sealed AGM

https://www.trojanbattery.com/product/motive-l16-agm/

[Ampster]

If you are concerned about safety have you considered Lithium? I just purchased 28 kWh of Lithium for $125 per kWh, delivered to my door in Northern California.

[SageOldmann]

Ampster as I said in my original post Lithium is out of the question due to cost right now. Maybe in a few years.....

[Ampster]

I understand. I don't presume know your desire to assemble a pack but when I saw that $1000 price tag for two 370 Ahr AGMs I couldn't help but do the math. Those AGMs are $225 per kWh.
In addition, because of their efficiency and larger depth of discharge you would not need the same capacity of Lithium batteries as you would need in AGM.

I am not trying to talk you into something you are uncomfortable with, but for the benefit of other readers. who may have the desire to DIY, I thought it might be useful to explain that there are less expensive alternatives.

[SageOldmann]

My suggestion, use the expensive, short lived AGM. Also, consider building the bank out of two series wired golf cart batteries (6v, 200ah) which solves the AGM "battery in parallel" problem. (AGM is so low resistance, that the parallel interconnect wires will steer power to one battery which will end up doing 80% of the work and fail earlier than expected)

Mike90250 I'm seeing dozens of posts all over the place where people use 2 banks of 2, 6 volt 225ah AGM batteries in series then both banks are wired parallel give them 12 volts with double the amps of just the one bank. One solar expert said.... "It is common practice to series then parallel connect lead acid, Lithium and other types of batteries. How you wire up larger banks of batteries is up for debate but four 6 volt batteries to make a 12 volt 450Ah battery is commonly done without problems."

Does this work or does the "parallel is a bad idea" come into play for this kind of set up as well? Will it still end up steering power to one battery bank more than the other?

[chrisski]

Mike90250 I'm seeing dozens of posts all over the place where people use 2 banks of 2, 6 volt 225ah AGM batteries in series then both banks are wired parallel give them 12 volts with double the amps of just the one bank. One solar expert said.... "It is common practice to series then parallel connect lead acid, Lithium and other types of batteries. How you wire up larger banks of batteries is up for debate but four 6 volt batteries to make a 12 volt 450Ah battery is commonly done without problems."

Does this work or does the "parallel is a bad idea" come into play for this kind of set up as well? Will it still end up steering power to one battery bank more than the other?

I'm choosing the battery system for what I'm building now. What caught me first is the "I have limited funds but have enough to bring my current system up to either of these levels." If you're on line power now, and only plan on using this for power outages, I really think you can get a brand new pair of Craftsman Inverter Generators at 2300 watts each, parallel them together with the accessory cords to 4100 watts total which may go through a gallon of gas total an hour, and run what you need when the power goes down for a whole lot less effort and money. My big assumption is you won't lose power more than 24 hours at a time and you have vehicle access to this place.

This system I'm building may not be the most rational decision, but I've decided I'm going to get 600 watts of panels on top of my RV to power a 1000 watt inverter powered by a 400 amp (type undetermined) battery bank. I will be able to watch all the TV I want with that, and I can make myself coffee out of an electric brewer, one cup at a time. I will also be able to microwave my popcorn. My fridge and water heater will both be gas.

[SageOldmann]

I have generators. They are for the heavy lifting like the furnace, fans, and refrigerator. Solar will be used daily with a pure sine wave inverter for tv, computer, ham shack etc and be available for them also in a power failure.

[chrisski]

Thanks. I do want to hear what you put in for batteries and read an update after they've been in for a while. For me, the batteries are the hardest choice.