Battery case corrosion is the most obvious of the visible battery aging factors, but if maintenance is poor, even relatively new batteries can fall prey to it. While corrosion is the most common battery damage seen, it is also the most easily prevented.
Corrosion occurs when sulfuric acid is left in contact with steel battery case materials for an extended period of time. If sulfuric acid is not regularly flushed out of the cells by overfilling (remember, electrolyte levels rise as the battery charges), and acid mist deposits are periodically washed off during seasonal battery maintenance, significant corrosion will not occur. Of course, very wet environments can promote rusting of the steel case, but this form of corrosion does not accelerate as quickly as that caused by acid, and it is rarely a factor in battery use.
Removal of paste or cement-like corrosion products which grow outward from battery case materials is a necessary maintenance step. Repainting of bare steel with an acid-resistant coating is also good for corrosion prevention.
Corrosion Forces Corrosion products left to grow on steel case surfaces can do their own damage to other battery components if this corrosion is not removed. Corrosion products that bridge the gap between case and cell-top connector straps can carry enough electrical current over time to burn, or carbonize, surfaces of plastic cell covers. Once this happens, removal of corrosion and washing of the battery will still leave behind an electrical pathway from connector to battery case. At this point, service by a battery technician is needed to remove all conductive deposits.
Moist corrosion products left on top of the battery can also erode lead connector straps to the point that they can no longer safely carry high battery currents. If any arcing or sparking occurs in the process of connector strap disintegration, it is an explosion hazard in the hydrogen/oxygen atmosphere near the cell vent cap openings.
Corrosion products take up a lot of space as they grow outward from the battery case, and they can exert a lot of pressure. Over time, these corrosion products can push in the side of a cell, break the cell container (jar) open, and destroy it. The weak point here is the cell jar to cell cover bond. Today’s batteries bond the cover in place by thermoplastically fusing it to the cell jar. The bond is strong, but it can be split open if enough force is applied. Once an opening is made, acid can flow out freely and further accelerate the corrosion process. Professional repair is urgently needed if damage gets to this point.
Corrosion of the positive post and its connections can be accelerated under wet conditions as a result of galvanic action. This can cause splitting of the cell cover around the positive post, making conditions even more favorable for continued corrosion by permitting acid seepage. Repairs must be made as soon as this damage is detected. Repairs of this type must be made by a trained technician because this work involves post drilling, careful removal of all corrosion products, possible replacement of the cell cover, and "lead burning" work on top of the battery to replace affected cell connector straps.
Once again, significant corrosion need not happen at all. The most basic attention to battery watering (don’t overfill), and a simple cleaning of the battery a few times a year will prevent corrosion from getting a start. Lead-acid batteries have a very low maintenance requirement.
Plate Growth Most batteries show evidence of “positive plate growth” as they age. This can be seen in the increase in height of the positive posts of the cells. Simple mechanical pressure due to this growth can cause damage. Cell covers can be pushed upward by this force, and either cracked or separated from the cell jar. Connector straps are put under stress by positive plate growth, and any weakness caused by corrosion may be aggravated. Evident damage from these stresses should be repaired by a trained technician, and any cracks in cell cover or jar should be sealed immediately.
Heating of battery components can cause damage, and this can be particularly evident in the cable end connector. Insulation of the cables can become cracked and brittle as a result of extended heating, requiring cable replacement. The source of heating is usually the connector housing and tips. No shortcuts should be taken here. If the connector area is heating up, replace all damaged components. You may have to replace the tips as well as the plastic connector housing if the heating problem continues.
For more information, contact Arcon Equipment Inc. (440) 232-1422.