Standard Procedure - Built-In Indicator Test
An indicator (hydrometer) built into the top of the battery case provides visual information for battery testing (Fig 1 ). Like a hydrometer, the built-in indicator measures the specific gravity of the battery electrolyte. The specific gravity of the electrolyte reveals the battery state-of-charge; however, it will not reveal the cranking capacity of the battery. A load test must be performed to determine the battery cranking capacity. Refer to STANDARD PROCEDURE for the proper battery load test procedures.
Before testing, visually inspect the battery for any-damage (a cracked case or cover, loose posts, etc.) that would cause the battery to be faulty. In order to obtain correct indications from the built-in indicator, it is important that the battery be level and have a clean sight glass. Additional light may be required to view the indicator. Do not use open flame as a source of additional light.
To read the built-in indicator, look into the sight glass and note the color of the indication (Fig 2 ). The battery condition that each color indicates is described in the following list:
- Green - Indicates 75% to 100% battery state-of-charge. The battery is adequately charged for further testing or return to service. If the starter will not crank for a minimum of fifteen seconds with a fully-charged battery, the battery must be load tested. Refer to STANDARD PROCEDURE for the proper battery load test procedures.
- Black or Dark - Indicates 0% to 75% battery state-of-charge. The battery is inadequately charged and must be charged until a green indication is visible in the sight glass (12.4 volts or more), before the battery is tested further or returned to service. Refer to STANDARD PROCEDURE for the proper battery charging procedures. Also refer to DIAGNOSIS AND TESTING - BATTERY for more information on the possible causes of the discharged battery condition.
- Clear or Bright - Indicates a low battery electrolyte level. The electrolyte level in the battery is below the built-in indicator. A maintenance-free battery with non-removable cell caps must be replaced if the electrolyte level is low. Water must be added to a low-maintenance battery with removable cell caps before it is charged. Refer to STANDARD PROCEDURE for the proper battery filling procedures. A low electrolyte level may be caused by an overcharging condition. Refer to GENERATORS & REGULATORS for the proper charging system diagnosis and testing procedures.