Since the electrolyte of a lead-acid battery consists of a mixture of water and sulfuric acid, the
specific gravity of the electrolyte will fall between 1.000 and 1.835. Normally, the electrolyte
for a battery is mixed such that the specific gravity is less than 1.350.
Specific gravity is measured with a
Figure 1 Simple Hydrometer
A simple hydrometer
consists of a glass float inside a glass
tube, as shown in Figure 1.
hydrometer float is weighted at one end
and sealed at both ends.
calibrated in specific gravity is positioned
lengthwise along the body of the float.
The float is placed inside the glass tube,
and the fluid to be tested is drawn into
the tube. As the fluid is drawn into the
tube, the hydrometer float will sink to a
certain level in the fluid. The extent to
which the hydrometer float protrudes
above the level of the fluid depends on
the specific gravity of the fluid. The
reading on the float scale at the surface
of the fluid is the specific gravity of the
An ampere-hour is defined as a current
of one ampere flowing for one hour. If
you multiply the current in amperes by
the time of flow in hours, the result is the
total number of ampere-hours. Ampere-
hours are normally used to indicate the
amount of energy a storage battery can