Ford Ranger Maintaince And Repair Manual page 66

HOW TO USE THIS BOOK
Maintenance−free batteries usually contain a built−in hydrometer to check fluid level
If the level is low, add only distilled water through the opening until the level is correct. Each cell must be
checked and filled individually. Distilled water should be used, because the chemicals and minerals found in
most drinking water are harmful to the battery and could significantly shorten its life.
If water is added in freezing weather, the vehicle should be driven several miles to allow the water to mix with
the electrolyte. Otherwise, the battery could freeze.
Although some maintenance−free batteries have removable cell caps, the electrolyte condition and level on all
sealed maintenance−free batteries must be checked using the built−in hydrometer "eye.'' The exact type of eye
will vary. But, most battery manufacturers, apply a sticker to the battery itself explaining the readings.
Although the readings from built−in hydrometers will vary, a green eye usually indicates a properly
charged battery with sufficient fluid level. A dark eye is normally an indicator of a battery with
sufficient fluid, but which is low in charge. A light or yellow eye usually indicates that electrolyte has
dropped below the necessary level. In this last case, sealed batteries with an insufficient electrolyte must
usually be discarded.
Checking the Specific Gravity
A hydrometer is required to check the specific gravity on all batteries that are not maintenance−free. On
batteries that are maintenance−free, the specific gravity is checked by observing the built−in hydrometer
"eye" on the top of the battery case.
52 BATTERY FLUID