December 2021 - 67

DIGITAL MULTIMETER
(DMM) TESTING
While DMM's (Figure 1) do not provide a
light-speed reaction to voltage variations
based on sample rate, they do provide a
stable enough reading to project static
voltage, continuous declines in voltage,
and charging system voltage output. One
major issue to consider is where to make
connection with the battery during such
readings. In knowing that battery voltage
is limited to connectivity between post
and terminal, I recommend comparing
post-to-post readings of battery voltage
to post-to-terminal readings. Note that
this process may be impacted by battery
design, such as side post batteries.
While slight variances do exist
amongst manufacturers to indicate a
battery's 100 percent state-of-charge, I
typically project 12.6V is the norm (leadacid).
While cranking, a measurement of
at or below 9.6V indicates severe battery
degradation or poor maintenance, and
further assessment must be conducted,
such as charge and re-test following battery
manufacturer's recommendations,
cell inspection (if serviceable), etc.
CONDUCTANCE TESTING
Conductance testers utilize battery source
voltage to measure current and infer resistive
values in a complex, yet simple manner.
This technology is similar to the use
of DMM's when performing basic testing
procedures (voltage, resistance, and current
measurements) to mathematically
project measurable outcomes. The major
benefits of utilizing conductance testers
to determine battery conditions are the
tool's cost and size. Conductance testers
(Figure 2) are traditionally handheld, consume
very little space, and are typically
less expensive than dedicated carts used
to assess battery condition. Conductance
tester manufacturers currently equip their
tools with exportable data files or immediate
printable results to document battery
condition at the time of measurement, and
often include summaries of battery design,
post arrangement (side/top/stud), voltage
p Figure 2 - Conductance test.
pFigure 3 - Load tester cart.
output, inferred amperage output, and battery
condition based on tool analysis. This
type of testing allows technicians to easily
document their findings and display evidentiary
results upon completing the test.
CASE STUDY: 2007 CHEVROLET
IMPALA
A customer came in complaining of a short
crank but no start after extended time sitting
- the car sat for four-plus months.
Because this vehicle had not been
started nor driven in months, I verified
the no crank/no start complaint. Turned
the key and nothing. I popped the hood
and used a DMM to check resting voltage
on the battery. I found 4.13V - less than
30 percent of an expected resting voltage
on a 12V (12.6V) battery. Knowing that
flooded lead-acid batteries have memory
issues if not maintained continuously, I
jump-started the vehicle with a battery
booster to measure charging system voltage
with the DMM, finding 13.81V when
running. After allowing the battery to
charge, I ran a conductance test to determine
the battery's condition. After charging,
the battery's resting voltage peaked
at 10.26V and only output 26 CCA's. The
battery was replaced and the vehicle operated
normally.
LOAD TESTING
One of the most stressful ways to assess a
battery's condition is by loading it to the
point of higher amperage output readings
upon testing. Load testers can be
handheld or cart based (Figure 3). They
may also be equipped with analog and/or
digital readouts that assist a technician in
documenting raw, measured values that
project battery condition. In a carbon
pile test, the battery is forced to conduct
through carbon elements under pressure
to measure live voltage and/or amperage.
As pressure increases on the carbon pile,
resistive value decreases and forces the
battery to exhaust itself of stored electrons
in an effort to project how stress impacts
the battery's performance. A major
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December 2021

Table of Contents for the Digital Edition of December 2021
