Batteries
Abnormal voltage levels
Infrequent use or overcharging causes abnormal voltage levels, which
can make it much harder for a car battery to function properly. When a
technician receives a repair request for a vehicle that won’t start, usually
the first task is to test the battery’s state of charge. Normal battery
voltage should be around 12.6 volts. Any voltage reading under 12.5
volts will raise an eyebrow, and a voltage reading significantly higher
than 12.6 volts may indicate the charging system is overcharging the
battery.
A recently-driven vehicle’s battery voltage might be a little higher due to
what’s called a surface charge, which can cause a reading that is a
couple tenths of a volt above normal. However, if the voltage is
noticeably above that, it indicates a potential problem with the charging
system.
A battery can also experience a certain degree of “self-discharge,”
which means that it isn’t recharged frequently enough and will
eventually lose some of its stored energy. Battery age can reduce the
“standby” length prior to a failure to start. If the vehicle hasn’t been
driven for four or five days, you can expect the voltage readings to be
low. Voltage loss will be determined by the number of components the
battery is supplying power to, its age and internal condition, ambient
temperature, and how long the vehicle has been sitting. However, a
charger at the correct setting can usually bring the battery back to life.!
Starting Test
Post start test voltage should not be below 10 volts.( 9.6V according to
tester documentation)
Should be around 11 volts for a good battery
Charging
Ripple voltage test not over 10%. 12v battery 100mV is highest it should
be.
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