When Is A 12V Battery Fully Charged; Hydrometer - Husqvarna 967187001 Workshop Manual

Batteries and maintenance
14.6 When is a 12V Battery Fully
Charged?
A fully charged battery keeps the rest potential
(unloaded) over 12.7 volts. Specific gravity is then
1.28. A battery that is principally empty holds a
rest potential of about 12 volts. Specific gravity is
then 1.20.
State of Battery voltage
charge (approximate)
100 %
75 % 12.37 Volt
50 % 12.05 Volt
25 % 11.65 Volt
Equal to or below
Discharged
11.4 volts.

14.7 Hydrometer

A hydrometer can be used to check the condition
of a battery, cell to cell if you have a battery with
free acid that can be accessed by opening the
caps. A fully charged battery has a specific gravity
of 1.28 and 75 % charged 1.23 and 50 % 1.18 and
25 % 1.14.
If a battery has a degree of charge at 50 %
(12.15 V) or a specific gravity at 50 % of 1.18
lower, it will start to "sulfate" and be destroyed.
In order to obtain a maximum service life from a
battery, it is essential to maintain a state of semi-
charged or higher (more than 50 % = 12.15V or
specific gravity of 1.18). If a battery is more than
50 % discharged, it is essential it be recharged
immediately.
When a battery begins to decay, it is called
sulfating. The more discharged a battery is, the
greater the risk of sulfating. The only way to avoid
sulfating is to charge the battery regularly. Then
the battery will survive its maximum service life.
When the battery is discharged, the lead and lead
oxide that was on the battery's lead plates turn to
lead sulfate. This lead sulfate in turn forms water
that dilutes the battery acid. That lead sulfate is
formed is a completely natural part of the process
inside a battery. When the battery is charged, the
sulfate turns to lead, lead oxide and sulfuric acid.
If the battery is left discharged, the crystals of lead
sulphate will form differently and so much that
they cannot be recreated when charging. Sulfating
has then taken place and the battery is probably
destroyed.
140
English –
Relative
density at
+15 degrees C
12.7 Volt 1.265...1.290
1.235...1.265
1.205...1.235
1.170...1.205
1.110...1.135