Electrical/Electronic Systems
Work Example 10

WorkKey Level: 4
NATEF Automotive Tasks: VI.B.1

Open-circuit voltage test (sealed batteries)

Your service manual states that the battery must pass the state-of-charge or open-circuit voltage test before a capacity test, which provides a realistic determination for battery replacement.  If the battery shows less than 12.2 volts, it should be recharged before the capacity test.  If the state of charge is 75% or more, the battery is considered charged. Using a digital multimeter (DMM) set on DC volts, you perform an "Open-circuit voltage test”, by checking the voltage across the positive and negative battery terminals.  The results of this test can indicate a battery’s state of charge.  You measure 11.8 volts at 80°F on the open-circuit voltage test.    

Open-Circuit Voltage	State of Charge at 800F
12.6 or greater	100%
12.4 to 12.6 volts	75% – 100%
12.2 to 12.4 volts	50% – 75%
11.7 to 12.0 volts	0% – 25%
11.7 or less	0%

 

 

 

 

a.  What voltage reading indicates a 100% charge?

b.  What does your reading indicate?

c.  What reading indicates a 75% charge?

d.  Should you recharge or replace the battery?

e.  How can you explain the need for a new battery to a customer?

Solution:

a.  12.6 volts or greater (Read from the chart.)

b.  Our reading of 11.8 volts indicates a 0% to 25% charge.

c.  12.4 volts (Read from the chart.)

d.  Recharge the battery first

e.  Answers will vary