Specific Gravity

WEEDING OUT A BAD BATTERY FROM YOUR PACK

Most electric golf cars utilize a battery pack of four or more deep-cycle batteries that can last a long time if you’ve performed the proper maintenance. Periodically, however, the vehicle may not seem to have the range it used to, and replacing all of the batteries may be cost-prohibitive at the moment. In most cases, it’s not the entire battery pack that is going bad, but instead, one battery is not keeping up with the rest of the pack and hurting performance.

Identifying A Bad Battery In Your Pack

1: Fully Charge Your Battery Pack And Take Readings

Perform a full charge to all the batteries and check the specific gravity readings on each battery with a hydrometer and multi-meter. Use the battery manufacturer’s data to see if the readings show the battery pack is undercharged. (Here’s an example of a typical deep-cycle battery data). Repeat the charge cycle to bring the state of charge of the pack up. If, after repeated charges, the batteries begin to increase in specific gravity readings, the problem is not the batteries, and further investigation is required.

2: Perform A Discharge Test At 50% DOD

If the specific gravities indicate charged batteries (1.260 or higher in all cells) and the voltage readings are good on each battery, discharge the battery pack on the vehicle in question. If one cell is significantly lower than the rest of the cells in the pack, mark that battery as suspect. Use a load tester or run the golf car through its typical routine. Battery packs that give less than 50-percent of the rated runtime are usually considered bad.

3: Test And Find The Bad Battery

Measure the voltage at the end of your discharge test to locate the bad battery. The one with a significantly lower voltage than the rest of the pack at the end of discharge is usually the culprit.

4: What If All The Batteries Show Low Voltage?

If all the batteries have a low voltage, and your hydrometer readings on all the batteries do not show a single defective cell, then the entire battery pack may be at the end of its service life.

Replacing Defective Batteries

Once you’ve found a bad battery in your golf car’s battery pack, it is okay to replace the single battery with a new one if it’s under six months old.  If the battery is over six months old, it’s 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.

When replacing a single battery or battery pack, it’s important to keep these facts in mind:

1) Cycle life comparisons should be made at the same depth of discharge (DOD).

2) Amp-hour ratings should be compared using the same discharge time and/or discharge current that will be used in the application.

3) Run-time ratings may be the most accurate comparison when selecting a battery for a given application.

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