Battery question

NAZranch · November 2020

Hi you guys.....
New to forum, long-time lurker, got me a problem.

I installed a system at my little off-grid cabin about 3 years ago. Good system, all Schneider.....went with SLA batteries, best I could afford at the time. Been working great! So I went out there last weekend and discovered the batteries would not hold a charge.....charge up ok during the day, but lose the charge as soon as the sun goes down. My son had gone out there and used a portable AC unit (with my permission), he said one night the batteries got drained really low.... I'm guessing by over-working the batteries, they have been damaged.

Are they damaged beyond repair? Any way to recharge and get more life out of them? IF not, should I just get some cheaper golf cart type batteries?

This cabin only gets used about once a month, so not critical, but it was sure nice having a fridge and lights...:-(

Thanks in advance for any advice...

Marc Kurth · November 2020

Details matter. Different battery types/brands tolerate abuse and others do not, SLA is a very broad description. Depending upon what you have, they may be very recoverable, or they may be ruined.

What do you have?

How long ago was the deep discharge, and how low was it?

Marc

NAZranch · November 2020

Thanks.... They are Leoch 6 V Sealed batteries. 8 of them x 6V each.

The discharge was in late July and they went down to about 20%

Sandroad · November 2020

I had a very similar same situation at my cabin with 8 sealed GC2 Centennial batteries that discharged too low for too long and sulphated. No recovery was possible so I recycled them (after just 2 years use) and went with LiFePO4.

BB. · November 2020

If they were at 20% state of charge for 2+ months--That is not good. If the system was recharged to back >90% the next day--Then that should not have "killed" them at that time.

Also depends on the exact model of battery... True deep cycle batteries can take that deep of cycle (with a quick recharge to >90% SoC).

If they are telecom battery designed for float service--They do not like being cycled down low.

What is the AH rating of your batteries (link to your model)?

If the system is running well--The best thing to do is turn of the breakers/switches to all loads, and just let the solars panels+charge controller manage the bank (make sure these are floating most of the time, and not somehow charging at absorb set point).

If you have snow in the winter, for Lead Acid batteries, it is sometimes better to just disconnect all loads and the charge controller, and let everything cold soak until spring... MPPT type charge controller with snow on the panels--Do not charge, and the MPPT controllers with their few watts of draw 24x7 can take a bank down after a few months of snow on the panels.

If you are around Phoenix or Prescott AZ, you are not going to get months of snow on the panels (I would guess).

-Bill

NAZranch · November 2020

Here is the info for my batteries...Thank you for the help!

Leoch DTA6224 6 volt 224 amp hour SLA Battery Price: $220 ea plus tax with exchange* (core charge of $20)
Bci Group Size: GC2 Replaces Deka 8AGC2, T-105RE, GPL-6CT

Terminal Type	Button
Amp Hours {AH}:	224 AH at 20 Hour Rate
Weight:	63 Lbs
Dimensions {L x W x H}	10.2 in x 7.09 in x 9.84 in
Initial Charging Current: Charging Voltage: Cycle Use Float Use	Max Current <45A 7.2-7.4v(Time 14-16Hr) 6.75-6.9v

BB. · November 2020

They seem to be "standard" AGM 6 volt @ 224 AH batteries. With a 1 year warranty and estimated 3 year life.

http://www.leoch.com/product/power/129.html

You can use flooded cell lead acid batteries for about 1/2 the price (rough guess)... And around 3-5 year life. "Golf Cart" batteries are 6 volt @ 200-240 AH or so (depending on brand).

-Bill

NAZranch · November 2020

But is there any way to 'fix' these is what I'm wondering.......

BB. · November 2020

The first answer is that suflation is a permanent loss of capacity... But, without taking a battery apart, only guessing that it is failing from sulfation vs corroded plate grids, cracked plates, eroded plates, loss of water from venting/over charging, etc...

One quick check for an AGM battery's physical health... Look at the positive terminal/post of the battery. If you see it "extruding" out the top of the case, then the positive plates are corroded (expanding from corrosion).

Second take--You have nothing to lose at this point, measure resting voltage, then try a reduced EQ voltage for a few hours at a time, let rest, then take resting voltage measurement and see if it rises. If the battery gets hot or starts "hissing" (gassing), stop and let cool, then try again...

https://forum.solar-electric.com/discussion/comment/410667#Comment_410667

Marc Kurth Solar Expert Posts: 830 ✭✭✭✭

July 10

Every AGM can be equalized, it's a matter of how much damage you will do. Concorde is the only one that specifically approves regular equalizing to recover lost capacity from less than ideal charging. As you likely recall, I have hands-on experience with literally thousands of both Concorde and Fullriver. At the risk of being repetitive, all AGMs are not the same and this applies to EQ also.

Sometimes it is a "lesser of evils" decision when trying to recover from severe undercharging. For a severe example, if equalizing takes a sulfated battery from 50% capacity to 90% capacity, I see that as a net gain - even though you permanently lost the top 10%. When trying to recover damaged Fullriver batteries, I would do exactly what you did: slightly lower EQ voltage for shorter time periods. Repeat until you see no appreciable gain in standing voltage.

With Concorde, I would go 62v (at 77F) for a full 8 hours. Doing this occasionally, will not cause any measurable damage. Note: Only EQ at the end of an Absorb phase, after dropping into Float.

Marc

Marc did not say in his post(s)--But I would guess that a reduced EQ voltage would be around 2.5% battery capacity for EQ current (or less)... No reason to cause excessive heating/gassing in a sealed battery (and cause more "unrelated" damage to batteries).

Note that Concorde is the only AGM battery mfg (that I know of--Which is not a lot), that recommends elevated EQ charging (62 volts @ 48 volt bank; or 15.5 volts for a @ 12 volt battery bank--etc.). Doing this for non-Concorde batteries will cook them.

Note that any EQ charging done should be monitored. There is always the chance of overheating (or worse) if the EQ is not done properly or for excessive periods of time... Especially when you are trying to EQ a sealed/AGM lead acid battery.

There are also Desufators... Whether they work or are witchcraft--Lots of people to argue all sides:

Here is a nice explination of how folks think they work and basic function:

http://www.barkeraircraft.com/files/Pulse3_web_layout_.pdf

And you can buy desulfators or battery chargers that have a desulfator function built in... I am not sure they work at all (or in a minority of "bad battery" situations)... But I am not in the business so I have no direct experience either way to back my opinion up.

https://www.amazon.com/s?k=desulfator

Battery Minders are good float chargers (I have a few of them and use them on cars that are not used very often). Some have a desulfator function (again, no idea if it helps or not).

There has been an issue seen with (an older Outback MPPT charger, as I recall) that had its charging current significantly reduced when charging a battery bank with a desulfator attached--Removed the desulfator, and the MPPT controller worked as expected again. (desulfators are "electrically noisy"). One data point...

-Bill

NAZranch · November 2020

Thank you for your comments. I will check the voltage next time out......!

Battery question

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