A NEEDLE TYPE HYDROMETER uses the
same principles as the ball type. When electrolyte is
drawn into the hydrometer, it causes the plastic needle
to register specific gravity.
A fully charged battery should have a hydrometer
reading of at least 1.265 or higher. If below 1.265, the
battery needs to be recharged. or it may be defective. A
discharged battery could be caused by the following:
Charging system problems
Starting system problems
Poor cable connections
Engine performance problems requiring
excessive cranking time
Electrical problems drawing current out of the
battery with the ignition OFF
defective battery can be found by using a
hydrometerto check each cell. If the specific gravity in
any cell varies excessively from other cells (25 to 50
points), the battery is bad. Cells with low readings may
be shorted. When all of the cells have equal specific
gravity, even if they are low, the battery can usually be
On maintenance-free batteries a charge indicator
eye shows the battery charge. The charge indicator
changes color with levels of battery charge. For
example, the indicator may be green with the battery
fully charged. It may turn black when discharged or
yellow when the battery needs to be replaced. If there is
no charge indicator eye or when in doubt of its
reliability, a voltmeter and ammeter or a load tester can
also be used to determine battery condition quickly.
As a mechanic you will be expected to test
batteries for proper operation and condition. These
tests are as follows:
Battery leakage test
Battery terminal test
Battery voltage test
Cell voltage test
Battery drain test
Battery load test (battery capacity test)
Quick charge test
BATTERY LEAKAGE TEST.A
leakage test will determine if current is discharging
across the top of the battery. A dirty battery can
discharge when not in use. This condition shortens
battery life and causes starting problems.
To perform a battery leakage test, set a voltmeter
on a low setting. Touch the probes on the battery, as
shown in figure 2-6. If any current is registered on the
voltmeter, the top of the battery needs to be cleaned.
BATTERY TERMINAL TEST.The battery
terminal test quickly checks for poor electrical
connection between the terminals and the battery
cables. A voltmeter is used to measure voltage drop
across terminals and cables.
To perform a battery terminal test (fig. 2-7),
connect the negative voltmeter lead to the battery cable
end. Touch the positive lead to the battery terminal.
With the ignition or injection system disabled so that
the engine will not start, crank the engine while
watching the voltmeter reading.
Figure 2-6.Battery leakage test.
Figure 2-7.Battery terminal test.