How do SGs change as batteries age?

WaterWheel · December 2016

My LA batteries are 14 months old now, carefully watered, EQ every 4-6 weeks and generally the cells are fairly close in SG after an EQ. After the first 2 months (broken in) the batteries averaged 1.277 SG. A year later the average SG after an EQ and 3 hr rest is now 1.268. I guess I could EQ the hell out of them but judging from SG readings during an EQ I don't think they would come up much more if I cooked them.

Is this normal for batteries as they age? As determined by SG reading I generally cycle between 93% SOC and 75% SOC daily, rarely getting below 65% SOC.

Photowhit · December 2016

Are you compensating for temperature? Even after 3 hours the battery might still be warm. particularly a large mass like a forklift battery. Might be part of the problem.

Chart here;
http://support.rollsbattery.com/support/solutions/articles/208145-specific-gravity-temperature-correction-factors

mike95490 · December 2016

The longer batteries sit less than 95% charged, the sulfur is starting to lock onto the plates. ReCharging forces it back into the solution and the SG goes up. Over time, a little bit more sulfur gets stuck on the plates, and becomes harder and harder to dissolve, and your SG slowly starts going down, Eventually so much sulfur gets trapped in the plates, the battery looses all usable capacity.

WaterWheel · December 2016

I use a hydrovolt SG meter so yes, measurements are temperature compensated.

A very knowledgeable member on this site (I think it was Bill or Vic ) put forward a strong argument that attempting to charge much over 90% SOC daily (excess water usage and heat) may not be the best thing. That combined with a call I made to the Crown battery manufacturer tech who wanted me to get above 1.265 at least several times a week has me currently allowing the batteries getting charged to about 1.265% SOC most days.

So I guess the question is as a battery ages is it normal to see capacity to drop about 4-5% a year?

Photowhit · December 2016

No not usually, I wonder now if you were sure the batteries were fully charged before you equalized?

I have a 5 yr old forklift battery of a lesser grade (GB) and 11 cells are fine in the 270-285 range when fully charged. I have one bad cell, that I think was poisoned. I've extended the absorb time to 3hrs now and the cell is maintaining a higher SG when the charger shuts down @ 1.255 I hope the next chance I get to equalize and monitor, will bring it up the little extra. I suspect it has lost a good bit of capacity even if brought back into line.

The equalizing cycle on a charge controller or a charger is just that, and good for a Maintenance equalizing when batteries are in good shape, it will help mix the electrolyte and do allow for some correction. Corrective equalizing will help remove sulfates that have hardened on the cell and either put them back into solution (ideal) or have them fall off and drop to the bottom of the cell(not so great). I would continue to equalize and see if your cells don't come up more. Corrective equalizing is done on a fully charged battery and SG is checked and recorded hourly. When no cell improves after 2 hours you are likely at the best recovery you can expect.

WaterWheel · December 2016

I shoot for about a 10 amp cutoff for absorb on the 790 amp/hr battery bank but that was only giving me about a 1.260 SG after 4 hrs.     Manufactures spec for absorb is 58.1v.     After talking to crown tech support last summer about low SGs after 4 1/2 hr absorb cycles  they suggested that I bump it up to 58.5v absorb but they warned me to keep an eye on things so that I didn't overcharge.       They wanted to see at least a 1.265 SG at the end of absorb but really didn't like me going above 58.1v for the absorb voltage.       It helped a little although I still had to keep it into absorb until about a 9 amp current at the end of absorb in order to get to 1.265 SG.       Even after equalizing I was noticing SGs were very slowly dropping ofer the months after equalizing so...

A few days ago I gave it 8 hrs of absorb over 2 days (batteries rested between absorb cycles, no load) at 59.1v.     The bank was drawing 7.5 amps at the end.        I then EQd for 4 hours at factory specified 61.9v but saw little change in SGs after the first 2 hrs.     Four hour rest before testing.        Average SG is now 1.271 so better but...   I think that's the limit.

What am I doing wrong?        I'm beginning to suspect that Crown has too low of an absorb voltage published and by following it for the first 10 months I had the batteries I may have damaged them by following their charging specifications.

After doing a bit of research for other battery manufacturers with L-16 batteries
Trojan says absorb at 59.2v
Rolls shows 60.0v absorb
Crown Deep Cycle wants 59.5v absorb
My Crown 6CRP525 paperwork wants 58.1v absorb.      Crown tech support on the phone was weary of going up to a 58.5v absorb.

westbranch · December 2016

Did you verify that that was the Voltage at the battery and not just the charger setting? A loose/warm/hot connection?
Try a longer absorb at 58.3V, for 16 hrs??? just trying to brain storm...
hth

WaterWheel · December 2016

Yes, With 2 different multi-meters and the Conext battery monitor. All 3 matched. I've also verified the charging amperage with a clamp meter.

westbranch · December 2016

I guess lengthening the Absorb time is next.... I really noticed the difference when I shortened the Absorb time this summer, early AM voltages were up to 2/10 ths lower with just the Fridge and Net (modem&router) on overnight so I moved it back up... guess I hit the sweet spot by accident, now I just drop the Abs Voltage in summer when I get tons of input... so don't get an over Abs event... which I got daily...

WaterWheel · December 2016

But with the ending absorb rate being about 1% of battery capacity while charging at a higher voltage the factory lists I would assume the SGs would be over 1.268 (95% SOC) instead of the 1.258 - 1.260 I'm currently seeing.

When the batteries were only 6 months old and I could get the SG up to 1.277 I didn't worry about it but now I can't get them all the way up.

Dave Angelini · December 2016

Around 2 weeks to the solstice on my calender? Just a guess but it sounds like you are overthinking this

westbranch · December 2016

In post #8 you EQ'ed. did you get a lot of mixing (bubbling)? How hot did the battery get?
Have you tried an EQ daily for 2 or 3 times?

with the ending absorb rate being about 1% of battery capacity
that being the case I think you will have to do A,B & C as a set

A) go closer to or equal to near zero % (EA 4 amps?) ie, stay in Absorb daily over the winter

B ) start at the recommended Absorb voltage [ and increase in increments of .2V if you are not happy (after the first week or so) ]

C) do an EQ with the gen every 2 to 3 days, or daily, to see if you can maintain or gain on the SG readings.

All this is a process of discovery. "The truth is out there..... somewhere'' Fox Mulder

hth

WaterWheel · December 2016

Dave Angelini said:

Around 2 weeks to the solstice on my calender? Just a guess but it sounds like you are overthinking this

I suspect you may be correct.

Last night we went out for 7 hrs so I used the mini split to heat the house with outside temperatures dropping below 30 while we were gone. It really dropped the batteries to the point to where I didn't enter absorb until 1pm today. Still, I'm very impressed with the mini-split. Thanks for your earlier posts about mini splits. Mine is primarily for cooling but is sure is nice for occasional heating.

WaterWheel · December 2016

westbranch said:

In post #8 you EQ'ed. did you get a lot of mixing (bubbling)? How hot did the battery get?
Have you tried an EQ daily for 2 or 3 times?

with the ending absorb rate being about 1% of battery capacity
that being the case I think you will have to do A,B & C as a set

A) go closer to or equal to near zero % (EA 4 amps?) ie, stay in Absorb daily over the winter

B ) start at the recommended Absorb voltage [ and increase in increments of .2V if you are not happy (after the first week or so) ]

C) do an EQ with the gen every 2 to 3 days, or daily, to see if you can maintain or gain on the SG readings.

All this is a process of discovery. "The truth is out there..... somewhere'' Fox Mulder

hth

A fair amount of bubbling while equalizing, The batteries went up from 58 degrees to 75 degrees during that long multiple absorb and EQ session.

In the past I've considered equalizing every few days but figure I would probably do more damage than good in the long run.

Thanks for helping with this.

mcgivor · December 2016

Somewhere I read that if the SG is low, a corrective equalization should be performed and this process can take upwards of 15 hours, with close monitoring temperature and SG. The author stated that the battery should not be cycled, hense no loads during or in between sessions as the prosess can take several days. The temperatures stated were in degrees celsius, and it was noted that above 45 deg.C to terminate if temperatures are rising. 70 deg F is an ideal starting point temperature, additionally it was stated that if the SG was not increasing after one hour of the maximum SG reading, there was no point in continuing the process.
What I've read, take it for what it is worth.

Dave Angelini · December 2016

WaterWheel said:

Dave Angelini said:

Around 2 weeks to the solstice on my calender? Just a guess but it sounds like you are overthinking this

I suspect you may be correct.

Last night we went out for 7 hrs so I used the mini split to heat the house with outside temperatures dropping below 30 while we were gone. It really dropped the batteries to the point to where I didn't enter absorb until 1pm today. Still, I'm very impressed with the mini-split. Thanks for your earlier posts about mini splits. Mine is primarily for cooling but is sure is nice for occasional heating.

You are welcome! The mini-splits are amazing to me still after 10 years. They save so much firewood and some are now at close to 5 times as efficient heating as resistance heating. Have a solstice back there!

How do SGs change as batteries age?

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