4. Remove The Surface Charge.

The surface charge, if not removed, will make a weak battery appear good or a good battery appear bad. Eliminate the surface charge by allowing the battery to sit for between four to twelve hours in a warm room.

5. Measure The State-Of-Charge.

To determine the battery's State-of-Charge with the battery's electrolyte temperature at 80° F (26.7° C), use the following table. The table assumes that a 1.265 specific gravity cell average and 12.65 VDC Open Circuit Voltage reading for a fully charged, wet, lead-acid battery.

If the electrolyte temperature is not 80° F (26.7° C), use the Temperature Compensation table to adjust the Open Circuit Voltage or Specific Gravity readings.

The Specific Gravity or Open Circuit Voltage readings for a battery at 100% State-of-Charge will vary by plate chemistry, so check the manufacturer's specifications for a fully charged battery.

For non-sealed batteries, check the specific gravity in each cell with a hydrometer and average cells readings. For sealed batteries, measure the Open Circuit Voltage across the battery terminals with a digital voltmeter. This is the only way you can determine the State-of-Charge. Some batteries have a built-in "Magic Eye" hydrometer, which only measures the State-of-Charge in ONE of its six cells. If the built-in indicator is clear, light yellow, or red, then the battery has a low electrolyte level and if non-sealed, should be refilled and recharged before proceeding.

If sealed, the battery is bad and should be replaced. If the State-of-Charge is BELOW 75% using either the specific gravity or voltage test or the built-in hydrometer indicates "bad" (usually dark or white), then the battery needs to be recharged BEFORE proceeding. You should replace the battery, if one or more of the following conditions occur: