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Thursday, October 22, 2009

Battery Capacity

My parents have a Cobra Class A motorhome with a problem. There is something going on between the alternator and the battery; the battery will not hold a charge. If you use the wipers or headlights or anything like that while driving you lose battery power until the whole thing dies. They have replaced the alternator, the battery and (we believe) the inverter, yet the problem persists. They currently have the whole thing jerry-rigged with a battery charger that is hooked into the generator. Any thoughts on what else could be causing the problem?
Kelly Barnes, (Brunswick, OH)

Kelly, battery problems seem to ever nag us. The first step in finding out why batteries seemingly discharge quickly is to analyze the battery itself. Severely sulfated batteries simply will not hold a charge compared to newer, fresher batteries. The degree of sulfation is proportionate to its ability to hold a charge. All batteries self-discharge, but sulfated plates quicken the rate. Find a shop in your area that has a carbon-pile battery load tester. This test will provide insight to the internal happenings of the battery.

Clean and tight electrical connections are also extremely important. Corrosive terminals and faulty butt splices and other connections all lead to early capacity loss. Also, determine if the battery has indeed been fully charged. Chances are the battery has not been given a chance to become completely charged. Motorhomes of that vintage are notorious for employing mediocre or even inadequate charging systems, including an undersized alternator. (A fully charged battery is one that, during an independent charging process, maximizes the specific gravity reading and then plateaus. In other words, the specific gravity refuses to rise any higher. After two hours in that state, the battery is then considered fully charged).

After the battery has been tested, then focus on the alternator itself. Alternators and converter/chargers back then did not have the technical algorithms available today for proper and complete automatic battery charging. Tests should also be performed on the individual battery circuits to determine if any drains exist. Some small, parasitic drains are normal, but when current leakages approach 700-800 milli-amps, something needs to be rectified. Obviously, a larger drain on a battery is even worse. A qualified professional RV technician can easily perform this test for you.

There is good news, however. Today there are aftermarket alternators and converter/chargers that increase the RVers ability to extend the electrical life in the batteries. Also, newer battery technology has improved battery performance and has minimized over-charging risks. It should be a consideration for all "serious" RVers of older coaches to upgrade to high-tech batteries, sophisticated three-step chargers and high output automotive alternators. Electrical woes will certainly be minimized and under proper usage, can be completely eliminated.

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