(UPS). This section will not cover the batteries,
but the tool required to check them. We will
discuss batteries in chapters 9 and 10 of this
A hydrometer measures active ingredients in
the electrolyte of the battery. The hydrometer
Do not fill the hydrometer too much so that the
measures the SPECIFIC GRAVlTY of the
float rises into the suction bulb.
electrolyte. Specific gravity is the ratio of the
Since the weight of the float is at its base, the
weight of the electrolyte to the weight of the same
float will rise to a point determined by the weight
volume of pure water. The electrolyte's active
of the electrolyte. If the electrolyte has a large
ingredients, such as sulfuric acid or potassium
concentration of active ingredient, the float will
hydroxide, are heavier than water. Because the
rise higher than if the electrolyte has a small
active ingredient is heavier than water, the more
concentration of active ingredient.
active ingredient there is in the electrolyte, the
To read the hydrometer, hold it in a vertical
heavier the electrolyte will be; the heavier the
position and take the reading at the level of the
electrolyte, the higher the specific gravity.
electrolyte. Refer to the manufacturer's technical
A hydrometer (fig. 3-40) is a glass syringe with
manual for battery specifications for the correct
a float inside it. The float is a sealed, hollow glass
specific gravity ranges.
tube weighted at one end. Marked on the side of
the float is a scale calibrated in specific gravity.
Use the suction bulb to draw the electrolyte into
water after each use to prevent inaccurate
the hydrometer. Make sure enough electrolyte is
readings. Do not use storage battery
drawn into the hydrometer for the float to rise.