Apple Performa 6400/180 - Manual (Page 210)

Additional Procedures Battery Verification - 2
1 Set the voltmeter to the
10 volts DC scale.
2 Hold the positive probe
of the voltmeter to the
positive end of the
battery and the negative
probe to the negative end
of the battery.
3 If the battery voltage is
below 3.0 volts, replace
the battery. Refer to
“Battery Replacement”
in this chapter.