MG MGA Twin Cam Workshop Manual page 194

After examining the battery, check the vent plugs, making sure that the air passages are clear.
Storage
If a battery is to be out of use for any length of time, it should first be fully charged and then given a
freshening charge about every fortnight.
A battery must never remain in a discharged condition, as the plates will become sulphated.
Initial filling and charging
When a new battery has been supplied dry it is necessary to fill the cells with electrolyte of the correct
specific gravity.
All batteries, including those having type suffix letter "Z" (e.g. SGZ, etc.) and those having no
additional suffix letter (e.g. SG, BT, etc.), are assembled with dry separators. The specific gravity of
the filling-in solution depends upon the climate in which the battery is to be used (i.e. 1.260 for
climates below 27° C. (80 F) and 1.210 for climates frequently above 27° C. (80 F). For more details of
the requirements of "dry-charged batteries see Section N.31.
The electrolyte is prepared by mixing distilled water and concentrated sulphuric acid 1835 S.G. The
mixing must be carried out in a lead-lined tank or a suitable glass or earthenware vessel. Steel or iron
containers must not be used. The acid must be added slowly to the water, while the mixture is stirred
with a glass rod. Never add the water to the acid, as the severity of the resulting chemical reaction
may have dangerous consequences.
Heat is produced by the mixture of acid and water, and it should, therefore, be allowed to cool before it
is poured into the battery, otherwise the plates, separators and moulded container may be damaged.
The temperature of the filling-in acid, battery and charging room should be above 0°C. (32°F.).
To produce electrolyte of the correct specific gravity:
To obtain specific gravity (corrected to 60°F
Carefully break the seals in the filling holes and half-fill each cell in the battery with dilute sulphuric
acid solution of the appropriate specific gravity (according to temperature). The quantity of electrolyte
required to half-fill a two-volt cell is ½ pint (0.28 litre). Allow to stand for at least six hours, then
complete the filling of the cells by the addition of more diluted acid of the same specific gravity as
before until the level reaches the bottom of the filling holes and allow the battery to stand for at least
another two hours before commencing the first charge.
Charge at a constant current of 35 amps. until the voltage and temperature-corrected specific gravity
readings show no increase over five successive hourly readings. This period is dependent upon the
length of time the battery has been stored since manufacture, and will be from 40 to 80 hours, but
usually not more than 60.
Throughout the charge the acid must be kept level with the tops of the separators in each cell by the
addition of electrolyte of the same specific gravity as the original filling-in acid.
If, during charge, the temperature of the acid in any cell of the battery reaches the maximum
permissible temperature of 38°C. (100°F) in a climate below 80° F. (27°C.) or 49° C. (120°F) in a
climate frequently above 80 F. (27° C), the charge must be interrupted and the battery temperature
allowed to fall at least 5.5°C. (10 F) before charging is resumed.
At the end of the first charge, i.e. when specific gravity and voltage measurements remain constant,
(16°C)
1.290
1.270
1.260
1.210
Add 1 part by volume of 1835 S.G. acid to
distilled water by volume as below
194
2 parts
2.7 parts
3 parts
4 parts
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