Diagnosing A Bad Deep-Cycle Battery

Finding The Weak Deep-Cycle Battery In Your Pack

There’s a time in the lifespan of a deep-cycle, flooded lead-acid battery where it will begin to fail and not hold a full charge.  Typically there’s no indication when this happens, other than when your battery-powered golf cart, aerial platform, forklift or floor cleaning machine slows down and stops operating. While deep-cycle batteries do often go beyond their advertised lifespan, they will eventually lose performance. A single tired battery in a battery pack can bring down the overall performance, so finding which battery is the culprit is vital to restoring the full potential of your vehicle.

Fully Charge the Battery Pack

Begin your diagnosis by completely charging the battery pack and checking each battery’s specific gravity readings with a hydrometer. Healthy batteries should have similar specific gravity readings in all cells.  If a battery has one or more cells with low specific gravity readings, it may be getting weak and nearing failure.  If all the batteries have low specific gravity readings, try performing an equalization charge.  If the specific gravity readings continue to increase with equalization charging, the problem may be the charger or the charging methods and not the batteries.  Equalization charging should be performed monthly on healthy batteries and more frequently if continuous undercharging is detected.

Perform a Full Discharge

After charging the batteries and the specific gravity readings indicate that all the batteries are fully charged, perform a discharge as the car would normally be used over the course of a day.  If the runtime is significantly shorter than normal, there may still be a weak battery in the pack.  Check the battery voltages and specific gravity readings and confirm that all connections are clean and tight.  If one battery is significantly lower than the rest, mark that battery as a suspect. If no low battery is found, use a load tester to perform a timed load test.  Battery packs that give less than 50% of the rated runtime are usually considered to be no longer serviceable.

Measure Voltage

Using a multimeter, measure the voltage at the end of the discharge test to locate a potentially bad battery. The one with a significantly lower voltage than the rest of the pack at the end of discharge is usually the culprit.  If all the batteries have low voltage and low runtime and your hydrometer readings on all the batteries don’t single out a bad battery or cell, then the entire battery pack may be at the end of its service life.

Replacing One Or More Batteries

If a bad battery is identified, it may not be necessary to replace the entire pack.  Battery manufacturers suggest that it is acceptable to replace one battery in the pack with a new one if it is under six months old.  If the battery is over six months old, it’s usually best to replace it with another battery from your fleet that has a date within six months of the rest of the pack or replace the entire pack.

For more information on deep-cycle batteries, run-time ratings, and maintenance tips to keep golf car batteries running longer, visit www.usbattery.com.

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