Advanced Battery Tips from Floor Equipment Experts

Open-Circuit Voltage Test

For accurate voltage readings, fully charge the batteries and do not charge or discharge the batteries for at least 6 hours but preferably 24 hours prior to testing.

1. Disconnect all loads from the batteries
2. Use a voltmeter to measure the voltage
3. Check the state of charge with the table below

If the battery registers below the given table values, then the battery should be replaced.

State of Charge (SOC) (%) – An expression of the present battery capacity as a percentage of maximum capacity. SOC is generally calculated using current integration to determine the change in battery capacity over time.

Depth of Discharge (DOD) (%) – The percentage of battery capacity that has been discharged expressed as a percentage of maximum capacity. A discharge to at least 80% DOD is referred to as a deep discharge.

• Healthy wet cell batteries will reach a maximum on-charge voltage of 2.5 to 2.6 volts per cell. Resting voltage of 2.12 per cell.
• Wet cell batteries should never be discharged below 1.75 volts per cell in normal operations.

Load Test

Load test shows how the baseline voltage reacts to demand. This can be tested in the following ways:

• This allows you to verify battery voltage without a voltmeter
• Take the specific gravity per cell, add .84 to the number and you should end up with the same as the voltage reading

AGM testing is different than wet testing because specific gravity cannot be tested.

1. Make sure the batteries are fully charged*
2. Obtain the voltage readings from each battery
3. Load test the batteries and record the results
4. If applicable, disconnect the onboard charger
5. Attach a volt meter and run the machine for 20 minutes under a full load**
6. After 20 minutes, document the voltage while under load
7. Continue to operate the equipment for an additional 5 minutes while watching the voltage
8. • *   The battery industry's standard level for AGM batteries is a maximum on-charge voltage measurement of 2.38 volts per cell (28.56V for a 24V system). Refer to Open-Circuit Voltage Test for further state of charge details.
   • ** Test procedures require a 20 minute runtime because the typical battery load tester does not apply a load long enough to notice quality errors in the manufacturing of new AGM batteries.

• Suspect batteries will often give a normal voltage reading while at rest. However, the voltage will decline rapidly or will be erratic while under load. This may take 15-30 minutes before the symptoms are exhibited. AGM batteries that are failing can give the impression of good performance for an extended period of time before exhibiting a rapid voltage decline while under load.
• The resting voltage (no load) will immediately rebound so testing the battery without a load will yield “healthy” results making it appear that batteries are fine. Once a load is reapplied and the battery pack voltage is monitored, the voltage will quickly fall and yield the packs actual voltage capacity.
• Healthy batteries will decline in a linear, predictable rate.

• Nearly all batteries will not reach full capacity until cycled 10-30 times. A brand new battery will have a capacity of about 5-10% less than the rated capacity.
• Lead-Acid batteries DO NOT have a memory, and the rumor that they should be fully discharged to avoid this “memory” is totally false and will lead to early battery failure.
• At around 10.5 volts, the specific gravity of the acid in the battery gets so low that there is very little left that it can do.
• Batteries in storage should be above 2.07 volts per cell. They will begin the process of internal sulfation at 2.07 volts. Batteries that drop below 2.0 volts per cell while in storage will suffer significant and irreversible damage.
• False Capacity - a battery can meet the voltage tests for being at full charge, yet be much lower than its original capacity. If plates are damaged, sulfated or partially gone from long use, the battery may give the appearance of being fully charged, but in reality acts like a battery of a much smaller size. This same thing can occur in AGM cells if they are overcharged and gaps or bubbles occur. What is left of the plates may be fully functional, but with only 20% of the plates left. Batteries usually go bad for other reasons before reaching this point, but it is something to be aware of if your batteries seem to test okay but lack capacity and go dead very quickly under load.
• Voltage readings will NOT tell you how good the battery condition is - only a sustained load test can do that.
• Battery life is directly related to how deep the battery is cycled each time. Most golf cart batteries are rated for about 550 cycles at 80% depth of discharge.

• Water should be added after fully charging the battery pack unless the water is too low and the plates are exposed.
• Plate thickness (of the positive plate) matters because of a factor called “positive grid corrosion”. This ranks among the top 3 reasons for battery failure. The positive (+) plate is what gets eaten away gradually over time, so eventually there is nothing left. It all falls to the bottom as sediment. Thicker plates are directly related to longer life, so other things being equal, the battery with the thickest plates will last the longest. The negative plate in the batteries expands somewhat during discharge, which is why nearly all batteries have separators, such as a glass mat or paper, which can be compressed.
• Wet batteries discharge 5-10% a month while AGM batteries discharge 2-3% a month.
• Older batteries self-discharge faster than new batteries. Older wet batteries may discharge as much as 7% a week. Older AGM may discharge 2% a week.
• Automotive batteries typically have plate about .040” thick, while forklift batteries may have plates more than .025” thick. This is almost 7 times as thick as auto batteries. The typical golf cart will have plates that are around .07 to .11” thick. US Battery and Trojan L-16 types are .090”. The Crown L-16HC size has .22” thick plates.

During use, small sulfate crystals form, but these are normal and not harmful to the batteries. During prolonged charge deprivation, the amorphous lead sulfate converts to a stable crystalline that deposit on the negative plates. This leads to the development of large crystals which reduce the battery’s active material and negatively impact capacity.