MAILBOX: Industrial Battery Redemption

Intermediate
While a different brand than the reader’s, industrial flooded lead-acid cells like these can be removed from their case for individual maintenance or replacement.

I’ve had my off-grid system for long enough now that I’m learning about battery-bank life span. I’ve recently learned how to recognize when batteries are no longer performing at their peak, what can be done to service them, and how some proper care and feeding can resurrect what appears to be a dying bank.

My battery bank is two 850 Ah, 24 V industrial batteries in parallel. These batteries were purchased new in 2010 and placed into service with a 2 kW PV array and a backup generator. Unfortunately, the manufacturer wasn’t forthcoming with good guidance about bulk, absorb, and equalization charge levels, so I made some educated guesses based on general battery research.

During the 2016-2017 winter, the generator began running more often, and the charge time (especially the bulk part) was shorter than it should have been. “Probably just a sign that the batteries are aging,” I thought. During watering, I also noted that the plate protector in one cell was a dull gray color—the plate protector in all of the other cells was red. I also noted that I hadn’t, by my recollection, actually watered this cell in months, but all of its peers were forever in need of topping off.

This is when I realized that there was something more problematic than age at work, and that some real investigation was needed. I used three different tactics to test the battery for relative health:

  • I used my voltmeter to test the bad cell relative to the other 11 cells in the battery. Sure enough, this cell, fresh off a generator charge, measured a half-volt below its neighbors (1.6 versus 2.1 V).
  • I disconnected the battery from the bank after a charge run, and let it sit idle for five days. In that time, the battery self-discharged from 25 V to 21.2 V.
  • I ordered a new hydrometer. Once it arrived, I measured the specific gravity of the cells after letting the battery sit idle for several hours. The neighboring cells measured at about 1.265, but my bad cell measured zero. Yes, zero.

I concluded that this cell had internally shorted between the plates and effectively killed my battery. While all this testing was being done, I also noted that my remaining batteries were not performing well on their own. The bank went through bulk charge quickly, and when drawn down, would get to 23.9 V and then, in minutes, crash to below 23.3 V and start a new charge cycle from the generator. I concluded that the only real option available was to squeeze whatever life was left in the remaining battery while I investigated the state of storage and figured out how I’d free up $7,000 to $10,000 for new batteries. I also investigated whether the manufacturer would replace the failed battery under warranty (seven years for industrial batteries seemed like a premature death).

While there was no warranty coverage, getting the battery serviced and replacing the bad cell was an option. The company referred me to a heavy equipment retailer (specializing in forklifts) about two hours away. The vendor assured me that they would be able to replace the bad cell, would inspect and (if needed) service the others. It would take only a few days and wouldn’t cost more than $700. My friends and I wrestled about 1,600 pounds of battery out of the battery room and onto a trailer.

Once we dropped them off, the repair process didn’t go quite as smoothly as I’d hoped. Highlights included, “My shop guys say there are three bad cells,” and “I have this battery in stock for only $3,800,” and “Just to even think about replacing the cell we have to charge a $900 inspection and test fee.” At this point, I concluded that unless the repair bill exceeded 50% of the replacement cost, I would proceed. “OK,” they told me, “we’ll send the battery to the specialist company we work with and won’t proceed with any work until after they do their inspection.” They replaced the one bad cell; all the other cells tested at nearly their “new” capacity of 850 Ah. The final repair bill was $1,250.

While the bad battery was being tested/repaired, I spoke with the manufacturer about proper charge tolerances on the batteries. All these years, I’d been undercharging them. The remaining battery, after only one solid equalization run, stopped cutting out at 23.9 V. Turns out, it just needed a good stirring of the electrolyte through equalization.

With the repaired battery back in the bank, I’m now back to six days at a time with no generator input. The beasts are performing like they’re new again. From this experience, I’ve learned a few things:

  • Industrial batteries can take a lot of abuse and still come back to life—with proper information from the battery vendor.
  • You can replace bad cells in industrial batteries!
  • If you’re going to get batteries serviced, be in direct communication with the repair people.
  • Equalize regularly, and to the values the vendor recommends!
  • Pay attention to how often you have to water each of the cells in a bank. A cell that doesn’t seem to get thirsty may be sucking energy and capacity out of the rest of the battery.
  • Pay attention to how often and how long your generator runs. Fast charge and discharge cycles can be a bad sign about your battery bank health.

Thank you very much to Home Power for the many informative articles about batteries and their proper care and feeding, and for making themselves available to bounce ideas off of.

Joe McCabe • Napa, California

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