What percentage of "solar batteries" expire due to a bad cell?

softdown

I suspect the number may be quite high. I also suspect the phenomenon could be greatly reduced by the manufacture of a high quality battery. 

Why do I feel this way you may ask. It is because every 8D that is waiting for the scrap yard was perfectly serviceable except for one bad cell, two bad cells in one case. One battery was pushed until it developed two bad cells. FWIW....that particular battery created a 2am power loss in the middle of July in an alpine desert. Bad cells poison the entire array. Two bad cells would seem to destroy the array output. Kind of like a short circuit in a way.

Currently still using three 8Ds that were manufactured in 2011. One is pretty good, the other two are fair to pretty good. Their only other value is scrap lead so I figure they help shoulder the burden for the better 8D batteries. Plus this is an experiment that I like to conduct. My childhood hero was Edison before I learned about Tesla.

Which leads to another subject for conjecture. At what point is it economic to pull a battery? Opinions will vary widely depending on whether one buys or sells batteries I bet.

mcgivor

Technically there is no reason why a single cell in a monoblock wold be any more prone to failure than a single cell would be in a different arrangement, baring internal bridge failure. What most likely is the case is a single cell begins to drift without notice, SG dropping gradually in its daily discharge/recharge cycles, being masked by the other 5 cells taking up the slack of the lazy cell, which begins to sulfate, manifesting over time whilst still appearing to have good voltage across all 6 cells. Regular SG readings of all cells would identify this, EQ would prevent the cell from drifting beyond the point of no return, or at least difficult return because it is possible to reverse the damage in some cases. It only takes a few deep discharges with poor recharges to begin the process which can happen in a much shorter time than one may think, days or weeks, if the afflicted cell is not the pilot cell measured for SG, assuming that method is utilized, then it would be allowed more time to continue its downward trend. Measuring all cell SG's on a regular basis is by far the best way to prevent this from happening in the first place, or at very least check a different cell every time. The amount of time and effort the operator of a system invests, will be directly rewarded by the reduction of problems related to...........ignorance, negligence or both?  
Oh, yes I have experienced this and have learned a valuable lesson.

Estragon

I suspect that like us, most batteries expire from a single critical failure as a proximate cause, but also like us, if the proximate failure didn't do us in, something else would. My objective, for my batteries, and for myself, is to have everything wear out at about the same time :-)

At 20, I would be prepared to undergo a lot of pretty unpleasant treatment to address a health issue if I was otherwise healthy. At 80, not so much. Similarly, I'd replace a dud cell/battery in an otherwise healthy young bank, but in an older bank I'd be making end-of-life arrangements.

Sulfation is a bit like a slow growing cancer - it'll kill you eventually, assuming something else doesn't get you first, and will make you pretty sick in the meantime. Batteries can also die of something more like a heart attack, when enough plate has shed to the bottom to short the cell. Baby a bank with low voltage absorb etc will likely mean a lingering demise of the first type, vs more aggressive charging regimes resulting in the second.

7 years is getting a bit long of tooth. If I was one of those 8Ds, I'd be getting my affairs in order.

Photowhit

I suspect 99.9% fail to a bad cell, but it usually is a slow process of weakening and lost capacity...lol.

mike95490

in any battery, 3 or 6 cells, ONE of the cells is going to fail before the others.  Maybe only days ahead of it's brothers, or months because of a defect.

softdown

My suspicion, as others mentioned, is that low voltage situations are highly prone to making a cell consider the ultimate futility of service. With four superb 8D's, I have yet to see battery voltage drop below 12.3. Easy living for solar batteries....so far. When I get two cloudy days in a row, that may challenge the bank a bit. 

I still have four 8D's of mediocre quality left over from my last bank using eight 8D's of mediocre quality. Remnants of a "beginners mistake".  Thinking I may wait until a bad cell develops before yanking. Unless, of course, SG drops below fair. 

Built in 2011....yes. But not placed into service for a few years. Stored in cool to cold conditions. Which reminds me, the bottom battery bank is cooler than the top bank was. The bottom batteries have fared much better. I think ~75% of my replacements went to the top bank. Wish I had kept detailed records of that.

Estragon

So the bottom "much cooler" bank got to laze around, while the top bank did all the work?

softdown

Estragon said:

So the bottom "much cooler" bank got to laze around, while the top bank did all the work?

They were parallel wired and a couple feet apart so I thought the load would be similar. You seem to be saying that the warmer batteries will shoulder most of the work burden. If true, the mediocre 8D's will continue to do most of the work since I placed the superior 8D's in a cooler room. Seems pretty intuitive now that you mention it. Electrons are more active as temperature increases.....to a point. 

A couple feet may represent a significant temperature difference when the lower bank is virtually sitting on a cool floor. 

Estragon

I was thinking the chemistry happens faster in the warm string. Apparent capacity would be higher on the warm string, and charging/floating voltages needed would be lower. Depending on charge settings, temp difference, and RTS (if any) location, that could mean overcharging the warm string and/or undercharging the cool one.