Batteries - Caution!

The active materials within a battery are lead and sulfuric acid. Lead compounds formed through the charging and discharging of the battery. The electrolyte composition by weight is 33% sulfuric acid; the remaining two thirds by weight are lead compounds. Sulfuric acid is most concentrated and at its heaviest specific gravity (sg) when the battery is fully charged, with concentrations as high as 40% sulfuric acid.

When a battery is charged, additional energy is "stored" in chemical changes within the electrolyte. As the battery is discharged, energy is "removed" through the reversal of these chemical changes. Fully charged, the positive plate is lead and the negative plate is coated with lead dioxide.

When the battery is substantially discharged, both the positive and negative plate coatings are converted to lead sulphate. At this point the sulfuric acid concentration may be less than 10%.

Caution!

The electrochemical energy of a fully charged battery is enough to vapourize over half of the battery materials.

Anthology of a Shorted Battery

What if a fully charged lead-acid battery cell is shorted? Hopefully the device shorting the battery is protected by a breaker or fuse; otherwise it becomes hot and melts or vapourizes the device, clearing the short. Within off-grid installations, there is enough energy available to vapourize copper buss bars, cables and other circuitry. Vapourizing copper has the same expansion rate as dynamite.

What happens if the short doesn’t clear itself? When a short is placed across a string of batteries, the resulting fault current will begin discharging all of the cells until one or several cells fail. Rarely do all cells fail at the same rate. The cells that have not failed dissipate their energy into the failed cells. Not only do the failed cells typically melt and give off vapours, but these failed cells can become arc furnaces due to the energy contribution from the rest of the battery string. Unless the battery fails in such a way as to disconnect the circuit the amount of energy dissipated in the failed cell(s) is usually enough to totally vapourize the whole battery.

If melting battery cells find ground, the circuit continuity is continued through the melted parts and the conductive object. This is typically called a battery fire. Toxic clouds of sulphuric acid mist, vapours and metals are present during this type of fire.

Always Treat Batteries with Extreme Caution and Respect

Under normal conditions with batteries your exposure includes hazardous substances and hazardous materials. Hydrogen gas may be released and accumulate to explosive levels.

Concentrated, sulfuric acid, lead and other materials may be easily transferred from the battery posts to other areas including the hands, equipment and eyes of a careless operator.

Make sure a tool cannot fall on top of your battery array

Always wear eye protection and wear protective gear.

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