Off-Grid Battery Care – It Happens to the Best of Us

Written by: Alan Smith

This past summer Backwoods had a visit from one of our retired co-workers, Terry.  While it is always good to have friends visit, the circumstances for his dropping by were less than ideal.

A small, catastrophic failure had led to the loss of a battery bank, two inverters, and a voltage converter.  Ultimately, the failure was traced back to a single nut and bolt in the battery bank cable connections, that had developed hidden corrosion over time.  Corrosion causes resistance to the flow of electricity, which in turn generates heat.  With enough corrosion, and enough current flow, the amount of heat generated can be sufficient to melt battery terminal connections; which is exactly what happened in Terry’s case.  The melted metal flowed between the negative and positive terminals of his industrial battery, causing a high power short that was beyond the capabilities of any of the circuit protection, resulting in the damage to the equipment.

Now keep in mind, Terry is one of the more detail-oriented people we’ve had here at Backwoods.  The discipline of a military background, along with critical thinking of an engineer, were still not enough to overlook one very tiny detail.  Terry does his mechanical maintenance on a routine schedule; checking for tightness in wiring connections, cleaning accumulated spray off battery tops, cleaning out dust and spider webs, and keeping his battery terminal posts coated with anti-corrosion paste.  This is not the type of person you’d expect to see such a failure.

Corroded terminal bolts, off grid battery care
The pictures below are the actual culprit, and one of the clean assemblies, for comparison.

So what happened?  It all boiled down to the battery terminal connections.  What Terry had NOT done, was dissembled the nut and bolts from the battery terminals and cables to check for internal, hidden corrosion.  It had been about 6 years since he had done that level of inspection.  When previously reviewed, the hardware had been thoroughly inspected, cleaned, and re-assembled, and then coated with anti-corrosion paste on the exterior.  In one of the 16 nut/bolt pairs, a small bit of contamination or moisture must have been left trapped inside.  Over the course of the next six years, the corrosion grew, contaminating the entire connection; but was NOT visible externally at all!

Terry has since replaced his lost equipment and is back in operation. The tale makes a strong case for what all solar electric systems owners should already know: system maintenance is essential to the health and longevity of the equipment.  Just because the lights are on and everything looks good on the surface, there is still no reason to not be thorough and diligent on your system care.