Battery suggestions for FX2524

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Battery suggestions for FX2524

Postby tbaker25 on Sat Mar 15, 2008 6:28 pm

700 watts of solar into MX60
Hub + Mate
12 Delco S2000 SLA (wet, not agm) = 24v @ 660ah @ 100hr rate.

I've been running this small system for a year or two. I have specific circuits running on this system via a separate breaker panel, with the rest of the house wired direct to grid.

These off-grid circuits draw around 1.5 - 1.8kwh per day.

The problem is that these Delco S2000's suck. They were cheap and I should have known better. I'm lucky if I get a full night out of them before the sun comes up. All my settings are in good shape and spec'd for the batteries. I've pulled the pack apart and run tests on each battery, only to confirm that the batteries suck.

I'm looking to upgrade to some real batteries. They will be in my basement, about 65 deg F year round, on cement. I really want to stay away from hydrogen venting in this space, so I'm looking at AGMs. What's the current word on AGM quality? Are they lasting? What's the brand and model that people are having the most success with?

Crewzr, your running MK's, right? Have they been working well?

Thanks for any input,
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Re: Battery suggestions for FX2524

Postby crewzer on Sun Mar 16, 2008 5:40 am


Thanks for asking about my AGM batteries. I have four Deka/MK 8A4D AGM batteries wired in series/parallel for 24 V x ~392 Ah. They’re housed with a bit of insulation in a Delta Packer 60 chest located in my garage. I’ve had ‘em for ~2-1/2 years now (time flies!), and they generally appear to be doing quite well.

See: ... -chest.htm

AGM batteries appear to have a quirk or two. One is that they seem to be a bit sluggish at dissipating surface charge when they’re cold. My batteries’ temperature drops to as low as 45 F in the winter, so I sometimes see some odd charger behavior. I don’t recall seeing this behavior at battery temps above ~60 F. Additionally, there used to be a bit of a charging voltage imbalance between batteries in the same series string. This was resolved using two PowerCheq modules, one between each series pair.

See: viewtopic.php?f=1&t=1750&hilit=powercheq

All in all, though, I’m pretty happy with the batteries. They’re efficient, they require essentially zero maintenance (I occasionally check terminal hardware torque, individual battery voltages, and listen for valve hissing during absorption charge stage), and they’re not vented. I took 188 Ah – a 48% discharge – out of ‘em a few nights ago while running a dehumidifier (a 28 A load on the batteries), and had no problems.

Prices are all over the place on these batteries, so it pays to shop around, especially at local battery warehouses. And, here's a link to a nice looking installation that sports twelve size 8D AGM batteries: viewtopic.php?f=24&t=2036

Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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Re: Battery suggestions for FX2524

Postby tbaker25 on Sun Mar 16, 2008 10:49 am

Thanks Jim. I'm getting conflicting information on AGM vs Gel.

In this document from East Penn , on page 10 it shows for a 25% DoD, the gel model having 2100 cycles and the AGM as having only 925. For roughly the same price, a 8G4D has more than double the usuable life of a 8A4D. East Penn does not seem to spec efficiencies. From googling around a bit, it seems that gels may have a 10-15% loss, and AGM's have around 4%?

Concorde's Sun Xtender quotes 4,800 cycles for 20% DoD for their IEC tests, and 2,800 for their more demanding tests. They also claim that their AGM's offer many more deep cycles than Gel.

Granted Concorde's batteries are more expensive, but why does the life expectancy seem to be reverse regarding the two technologies? Penn says Gels last longer, Concorde (and every 3-rd party site I looked at) says that AGM's last longer.

I'm getting confused... :-)

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Re: Battery suggestions for FX2524

Postby crewzer on Mon Mar 17, 2008 5:58 am


Off the top of my head, my recollection is that VRLA batteries (both AGM and gel) are ~90% efficient overall (Wh out / Wh in), and their coulombic efficiency (Ah out / Ah in) is ~98%.

Yeah, the “cycle” specs can inded be corn-fuzing. As you’ve noted, East Penn (Deka and MK) cycle specs for their AGM batteries are rather dismal compared to their gel specs. Similarly, Trojan has published some nice technical info and specs for their gel batteries, but I’m not able to find corresponding info on their AGM batteries.

And: ... tSheet.pdf

Reading between the lines, Trojan seems to have different applications in mind for their various VRLA batteries. Specifically, it seems to me that their gel batteries are aimed at deep-cycle applications, and their AGM batteries appear to be aimed at so-called “dual purpose” applications. Like their “hybrid” Marine/RV FLA battery cousins, I suspect that “dual purpose” AGM batteries would not excel at either deep-cycle applications nor cold weather engine starting.

On the other hand, purpose-built deep-cycle AGM batteries from Concorde and Exide (i.e., GNB Absolyte IIP) seem to offer excellent cycle specs.

See: ... _62_61.pdf

My recollection is that I chose Deka’s AGM batteries over their gel’s for several reasons: (1) higher energy density, (2) higher surge capacity (handy for starting compressors), and (3) superior cold temperature performance (my batteries are in my garage, where winter temp drops to ~45 F on the “warm” wall). But, considering that my next battery bank may be 48 V x ~1,000 Ah, gel batteries may be the better choice at that time.

All in all, I’m pretty happy so far with the AGM batteries. Based on Deka’s specs, my typical discharge (~15%), and their generally cool environment, I expect to get >2,000 cycles from the battery bank, or ~7 years or so. I plan to conduct and publish a capacity test later this year after the battery temp reaches a stable and consistent 77 F / 25 C. That’ll probably be in July or August.

Jim / crewzer
090805 System Configuration: 966 W STC (849 W CEC PTC) 48V PV array, FM80, 24V x 400 Ah AGM battery bank, FX2524T w/ BTS, Hub-4 & Mate; Link-10 w/ BTS, & E-Panel.
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problems with DEKA 8A4D batts

Postby Hidrologo on Thu Sep 19, 2013 2:12 pm

This message regards the DEKA 8A4D batteries. I purchased 4 for my 48V 2kw system in April.
The house occupant during the summer complained that the batteries typically discharged overnight to the point where the system shutdown.
I have confirmed that this is the case. I have taken the batteries to the local company where I had them load tested, and they claim that they are good and that they arrived with less than a full charge.
Upon reciept of the fully charged batteries from the distributor, I again found that they almost discharge entirely overnight with effectively only a refrigerator and a few low watt lights. These batteries have been charged at absorb 56.8 V and float 54.2 during the summer.
I took the following data upon receipt of the batteries:
time V_batt notes
4.45pm 50.6V installed with no load from the house
4.46pm 49.6 installed with house load (refrigerator)
6pm 49.6 refrig. load
8:09pm 49.1 Refrig. + light or two
9:53pm 48.6 above with shower (Grundfos water pump, about 10 minutes)
2.56am 47.7 fridge only
7:40am 45.0 sunrise (red light on inverter)
9:19am 51.5 inverter green light, charging.

My view is that the AGMs are defective. They are not holding a charge even for a light load. Am I wrong?

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My RE system: Off grid, 2kW system 12 Mitsubishi 165 W panels, 4 12V Deka AGM 8A4D batteries in series (48V), GFX 3548 inverter, MX-60 Mppt controller, HUB 4 and Mate.

Re: Battery suggestions for FX2524

Postby BlackCherry04 on Thu Sep 19, 2013 5:04 pm

Well you only have 200 amp hrs of battery ( 100 amps hrs @ 50% dod, here is 50% " 2.56am 47.7 fridge only " ) and sounds like your using them like you have 400. Your charge voltage is low ( Should be at least 57.6 till you reach 2 % of capacity ) and who knows what else is wrong. Anytime your pulling your batteries to the LBCO ( Shut down ), you can only do it so many times till your batteries are shot.

" Warranty void if opened or improperly charged. Caution: Constant under- or overcharging
will damage any battery and shorten its life. Use a good constant potential,
voltage-regulated charger. For 12-volt batteries, charge to at least 14.4 volts but no
more than 14.6 volts at 68°F (20°C)
. Do not charge in a sealed container. The SAT
Series has more capacity at high discharge rates than conventional deep cycle batteries." ... ka-AGM.pdf

You really need a Battery Monitor with a Shunt so you can watch the Amps in and out of your batteries. Using voltage alone is big mistake. The Outback FNDC can do that and there lot's of others that make it simple.
Last edited by BlackCherry04 on Thu Sep 19, 2013 8:50 pm, edited 1 time in total.
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Re: Battery suggestions for FX2524

Postby Vic on Thu Sep 19, 2013 6:03 pm

The Deka 8A4D AGMs appear to want an optimum Absorb voltage of 14.3, and a Float voltage of 13.4 per 12 V battery:

AGMs do not have great cycle life for deep discharges -- 320 rated cycles to 50% State Of Charge, and only 200 cycles to 20% SOC.

Be certain to use a Battery Temp Sensor.

Refrigerators come in many sizes and efficiencies. So the load that this represents is not at all specific. Also, the run time will depend on how warm its environment is.

This IS a fairly small battery bank, especially for AGMs (which do not like deep cycles). And make certain that you have enough Absorption time to fully recharge the batteries.

If you are in the US, a Kill-A-Watt will help actual loads to be determined. FWIW, Vic
4/20/08: 18 Shell SQ 175-106 Vmpp, Stacked 5548 SW+, 1350 AH Surrette 4KS25's, MX-60, Kubota SQ-3250 25 KVA Polyphase Diesel genset. Thanks OutBack for this Forum + the great Support and Service.
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