SECTION 55 - ELECTRICAL SYSTEM 161
7.4 MAINTENANCE
SPECIFIC GRAVITY
The specific gravity of the battery electrolyte indi-
cates the state of charge.
Fully charged the specific gravity of the electrolyte is
1.280 minimum at 25 °C.
Alternatively the approximate state of charge can be
measured by using an accurate digital volt meter (+/
-0.01 V) as follows:
Less than ................. 10.5 V Battery unserviceable*
Less than ....................... 11.8 V Battery discharged
Less than ......................12.3 V Battery 1/2 charged
Better than .................. 12.6 V Battery fully charged
* See note under tests for possible recovery of a
mildly sulphated battery.
Battery voltage to be taken with the battery unload-
ed and:
A. After the battery has rested unloaded for at least
4 hours.
B. If the vehicle has recently run or battery has re-
cently been charged, switch on headlamps for 2
minutes.
When a battery discharges, sulphuric acid in the
electrolyte combines chemically with the plates and
this action lowers the specific gravity of the solution.
A battery hydrometer will determine the specific
gravity of the electrolyte in a cell and the amount of
unused sulphuric acid in the solution is a measure of
the degree of charge of that cell.
The lower the temperature at which a battery is re-
quired to operate, the more necessary it is that the
battery is maintained in a fully charged condition.
For example, a battery with a low specific gravity of
1.225 at 27 °C will operate the starting motor at
warm ambient temperatures, but may not be able to
do it at low temperatures due to a lower battery effi-
ciency.
Table shows the effect of temperature on the effi-
ciency of a typical battery.
Maximum battery life will be obtained if the correct
care and periodic inspection is given. It is important
that output capacity should not be exceeded by con-
stant and excessive overloading and that charging
requirements are maintained.
MAINTENANCE
SWARNING
Battery electrolyte causes severe burns. The bat-
tery contains sulphuric acid. Avoid any contact with
the skin, eyes or clothing.
Antidote:
EXTERNAL: rinse well with water, removing any
soiled clothing.
INTERNAL: avoid vomiting. Drink water to rinse
your mouth. Consult a doctor.
EYES: rinse abundantly with water for 15 minutes
and consult a doctor.
Battery terminal tightness check ... Every 250 hours
Electrolyte level inspection.......... Every 1000 hours
When servicing a battery the following steps should
be observed:
Z Maintain the electrolyte to the recommended level
of 6 mm above the plates. If this is not observed
the acid will reach a high concentration that will
damage the separators and impair the perform-
ance of the plates.
Z Use only distilled or de-mineralized water, do not
overfill and never use tap water or water from a
rain barrel or other source.
Z Always keep the battery at least 75% charged oth-
erwise the plates will become sulphated and loss
of efficiency will result with possible damage from
freezing at low temperatures.
Z Avoid overcharging the battery as excessive
charging will create high internal heat that will
cause plate grid deterioration and produce water
loss.
Z When fast charging ensure the battery tempera-
ture does not exceed 50 °C.
Z Do not add sulphuric acid to a cell unless the elec-
trolyte has been lost through spilling. Before re-
plenishing ensure the solution is at the correct
specific gravity. A slow charge is the only method
to be employed to fully charge a battery. A high
rate charger can be used to quickly boost the bat-
tery capacity but this must be followed by a slow
charge rate to bring the battery to full capacity.
Temperature Efficiency of a fully
charged battery
temperature
25.0 °C
-4.5 °C
-24.0 °C
-27.5 °C
-31.0 °C
-34.5 °C
-37.5 °C
100%
82%
64%
58%
50%
40%
33%
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