Subaru 2002 IMPREZA Service Manual page 431

3. SPECIFIC GRAVITY OF ELECTROLYTE:
1) Measure the specific gravity of electrolyte using
a hydrometer and a thermometer.
Specific gravity varies with temperature of electro-
lyte so that it must be corrected at 20°C (68°F) us-
ing the following equation:
= St + 0.0007 × × × × (t − − − − 20)
S
20
S : Specific gravity corrected at electrolyte
20
temperature of 20 ° ° ° ° C
St : Measured specific gravity
t : Measured temperature ( ° ° ° ° C)
Determine whether or not battery must be
charged, according to corrected specific
gravity.
Standard specific gravity: 1.220 — 1.290 [at
20 ° ° ° ° C (68 ° ° ° ° F)]
2) Measuring the specific gravity of the electrolyte
in battery will disclose the state of charge of bat-
tery. The relation between specific gravity and state
of charge is as shown in the figure.
D: MEASUREMENT
WARNING:
• Do not bring an open flame close to the bat-
tery at this time.
CAUTION:
• Prior to charging, corroded terminals should
be cleaned with a brush and common baking
soda solution.
• Be careful since the battery electrolyte over-
flows while charging the battery.
• Observe the instructions when handling bat-
tery charger.
• Before charging the battery on vehicle, dis-
connect battery ground terminal. Failure to fol-
low this rule may damage alternator's diodes or
other electrical units.
BATTERY
1. JUDGMENT OF BATTERY IN CHARGED
CONDITION
1) Specific gravity of electrolyte is held at a specific
value in a range from 1.250 to 1.290 for more than
one hour.
2) Voltage per battery cell is held at a specific value
in a range from 2.5 to 2.8 volts for more than one
hour.
2. CHECK HYDROMETER FOR STATE OF
CHARGE
Hydrometer
indicator
Green dot
Dark dot
Clear dot
*: Check electrical system before replacement.
3. NORMAL CHARGING
Charge the battery at current value specified by
manufacturer or at approx. 1/10 of battery's am-
pere-hour rating.
4. QUICK CHARGING
Quick charging is a method in which the battery is
G6M0103
charged in a short period of time with a relatively
large current by using a quick charger.
Since a large current flow raises electrolyte temper-
ature, the battery is subject to damage if large cur-
rent is used for prolonged time. For this reason, the
quick charging must be carried out within a current
range that will not increase the electrolyte temper-
ature above 40°C (104°F).
It should be also remembered that the quick charg-
ing is a temporary means to bring battery voltage
up to a fair value and, as a rule, a battery should be
charged slowly with a low current.
CAUTION:
• Observe the items in 1. NORMAL CHARGING.
• Never use more than 10 amperes when
charging the battery because that will shorten
battery life.
SC-21
STARTING/CHARGING SYSTEMS
State of charge Required action
Above 65% Load test
Below 65% Charge battery
Replace battery*
Low electrolyte
(If cranking complaint)