Wash the hydrometer barrel and float with soap and water on a regular basis. Rinse
thoroughly with water after washing to prevent soap transfer to the battery
electrolyte.
The change in specific gravity of the acid is directly proportional to the ampere hours
taken out of the cell on discharge.
The minimum recommended specific gravity is 1.140. Select a different pilot cell
each month to serve as a useful, general indicator of the condition of the battery
during charge and discharge.
Note:
The specific gravity of a cell will decrease with any increase in temperature.
Always record the electrolyte temperature when specific gravity readings are taken.
TEMPERATURE CORRECTION OF SPECIFIC GRAVITIES
All specific gravities quoted relate to temperature at 25
o
C and have to be corrected if
read at other electrolyte temperatures.
Specific gravities decrease as the temperature increases. To provide a standard, the
specific gravity can be corrected to 25
o
C in the following manner:
Take the temperature of the electrolyte and
• add 7 points (0.007) to the specific gravity reading for every 10
o
C above 25
o
C or
• subtract 7 points (0.007) from the specific gravity reading for every 10
o
C below
25
o
C.
For example:
A reading of 1.255 at 35
o
C corrected to 25
o
C gives 1.255 + 0.007 = 1.262
or
A reading of 1.275 at 15
o
C corrected to 25
o
C gives 1.275 - 0.007 = 1.268
ADJUSTMENT OF ELECTROLYTE SPECIFIC GRAVITY
Charge the battery at the equalising rate until specific gravities have been constant
over three successive readings taken at hourly intervals.
Should the specific gravity be high, remove a little of the electrolyte and replace
with an equal volume of distilled or deionised water. Add a small amount at a time,
forcing it well down into the cell, with the cells gassing, to help mix the water with the
acid. Allow the electrolyte to thoroughly mix by leaving on a vigorous gassing charge
for at least 1 hour. When mixed, read the specific gravity. Repeat this process until
the specific gravity is within the specified tolerance.
It is essential that the battery has been on charge at a voltage high enough to cause
vigorous gassing over 3 hours with no increase in specific gravity before attempting
to adjust the specific gravity upwards. If in doubt First National Battery should be
contacted for advice. When these conditions have been met and specific gravity is
still low remove a little of the electrolyte and replace with an equal volume of stronger
sulphuric acid (e.g. 1.400) while agitating as described above. Once again, repeat
the process until the specified tolerance is achieved.
When the adjustment has been completed, ensure that the level of the electrolyte in
each cell is correct by removing excess acid or topping up to the correct level with
acid of the same specific gravity.
