When cordless tools first entered the jobsite in the early
1980s, few thought they’d ever be able to compete
with their “tailed” counterparts. But as batteries
leapfrogged from 6 volts to 12 to 24 volts, users discovered
there was little these “tail-less apprentices”
couldn’t do. Today, cordless tools are the hottest-selling
tools for both professionals and D-I-Y’ers. This year,
more than 2 million new cordless drills
alone will hit the jobsite.
According to Jason Goger, a product
specialist at DeWALT Industrial Tool
Company battery and charger technology
is the heart of the cordless revolution.
Understanding batteries and chargers
can help you select the best tool for
your own type of work, and also help
you protect your cordless tool investment.
Making Sense of Volts
The most noticeable advance in cordless
tools is the ever-increasing voltage rating.
The higher the voltage, the more
power available at a given moment to
perform the task at hand. “Higher voltage equals more energy to the motor,
which means the ability to drive bigger
bits and blades,” Goger says.
Despite what you may hear, bigger (voltage)
isn’t always better. Plumbers, electricians
and other tradesmen who run
large spade bits, hole saws and auger bits
may need the brute force of an 18- or
24-volt tool, but if you don’t handle that
kind of work, a better option may be a
compact and lightweight 12- or 14.4-
volt model. “Larger tools don’t necessarily
do the smaller tasks any better than
a smaller tool,” Goger says. “It’s like driving
a dump truck versus a compact car
to the mall. Both will get you there, but
the smaller car is more efficient for the
task.” Goger also points out that smaller,
lighter battery packs can sometimes
be more comfortable to work with and
are easier to use in tight spaces where
bigger tools can’t fit.
After voltage, a specification to consider
is the Amp-hour rating, a general
number that categorizes how much
operating capacity a battery has when
fully charged. “If voltage is compared to
the size of a vehicle’s engine, then Amp hours
is like the size of the gas tank,”
Goger explains. All other factors being
equal, a higher Amp-hour rating (they
range from 1.2 to as high as 3.5) generally
means a cordless tool can run longer
or do more work per charge. It doesn’t
make the tool more powerful, it simply
provides the capacity to run longer
between charging.
But even within the same voltage and
Amp-hour ratings, Goger adds that
actual performance can vary greatly
between tools. “Consider what’s inside NiCd or NiMH Batteries?
the tool,” Goger says, referring to the
motor, transmission and other compo-nents
that share the work. “A significant
percentage of a tool’s potential can be
lost within the inside mechanisms,” he
says. Details such as high-quality magnets
in the motor, metal gears and carbide
chucks ensure that power is transferred
efficiently from the battery to the
bit or blade. What’s inside the battery
pack is also important. Compared to
professional batteries, the cells within
consumer-grade batteries may degrade
after as few as 20 recharges. Without
actually dismantling the battery, the
only way to ensure you’re getting the
power you paid for is to stick with professional
quality tools.
NiCd or NiMH Batteries?
Until recently, nickel-cadmium (NiCd)
batteries powered all cordless tools. But
some manufacturers have started experimenting
with nickel metal hydride batteries
(NiMH) as another potential power
source. In terms of Amp-hours, or
run-time, NiMH ratings have a slight
advantage, going up to 3 Amp-hours.
The highest-Amp hour rating for NiCds
is 2.4, but the potential is there to go
higher.
Unfortunately, NiMH batteries currently
have disadvantages that stand out
on the job site. For starters, NiMHs are
more temperature sensitive; the batteries
may not work in temperatures below
32 degrees F, and begin to degrade
quickly when exposed to temperatures
above 105 degrees. Comparatively,
NiCds can be used in higher temperatures
without compromising cell life.
Comparison tests also show that NiMH
batteries last for only about half the
number of recharge cycles as NiCd cells,
which means NiMH cordless tool users
could end up purchasing replacement
barteries more often.
NiMH technology is advancing and
may be more viable in the future, but
many tool manufacturers continue to
use NiCds because they offer the things
that matter most to cordless tool users
better performance and longer pack
life at a lower cost than NiMHs. Environmentally
conscious buyers may point
out that NiMHs are less toxic, but battery
recycling boxes at home centers and
electronic stores now provide an easy and
safe way to dispose of used batteries.
Charge It!
Because battery chargers don’t appear to
be doing any real work, they aren’t given
much attention. However, without
them, cordless tools would quickly
become paperweights. Understanding
how chargers work can help protect
your tool investment.
Not all chargers are created equal.
“Basic” chargers provide a continuous
charge for a given period of time regardless
of the battery’s status. This means
that once a battery is fully charged, the
charger keeps pouring energy into the
pack. This unneeded energy translates
into unwanted heat, which reduces the
overall number of recharges a battery
can take. Other basic chargers may have
a thermal switch that shuts off the charger
at a given temperature to prevent
overheating. But recharging a warm battery
will fool the charger into shutting
off prematurely, In this case, the charger
will indicate that a battery is charged
even when it’s not. The latest generation
“smart” chargers have a built-in microprocessor
that diagnoses the battery,
then delivers the optimum charge.
Smart charging is done in stages. First,
the charger waits for the battery to cool
before starting the “charging cycle.”
With some chargers, like DeWALT’s
newest 24-volt model, a fan cools the
pack and dissipates heat so the battery
can charge faster. Next, the charger performs
a “fast charge.” Because the cells
may charge at different rates, this stage
shuts off to minimize heat build up as
the fastest charging cells reach near-maximum
capacity. In the “equalization
stage” the charger balances, or tops off,
all the cells using a slower charge
designed to add power without bringing
heat. This process is like filling an ice
cube tray, when you gradually turn the
faucet back as water spreads into each
cube opening. Lastly, a “trickle charge”
replaces power ordinarily lost during
periods of non-use when the battery is
stored in the charger.
Debunking Battery Myths
Myth 1: Batteries have a memory effect.
Tradespeople have passed along the
myth that battery packs must be fully
drained before recharging. According
Goger, that “memory” myth is based on
cordless tools in a previous era. “Back in
the 1980s, it was possible to inadvertently
limit battery capacity by methodically
using a tool and draining the battery
the same way over and over again,”
Goger says. But he adds, “Battery memory
isn’t an issue today because technology
has improved and tools are used for
a greater variety of tasks.”
Back then, the “cure” was to clamp or
tape the tool’s trigger and completely
drain the battery before recharging. In
reality, taping a trigger to use up every
last electron does more harm than good.
“When the battery drains, the weaker
cells empty first,” Goger says. “The
stronger cells continue to operate, but
the drained cells could actually reverse
polarity.” Reversed-polarity cells no
longer accept a charge. This means a
freshly charged 12-cell pack will only
have 11 cells working—meaning shorter
run time, less power and faster degradation
of the remaining cells.
The best advice for cordless tool users is
simply to recharge a battery as soon as
they observe a drop in performance, and
to keep the battery in the charger until
it’s needed.
Myth 2: Keep batteries in the freezer. In
truth, storing those extra batteries for
your camera or flashlight in the cold
may help keep them fresher than in a
drawer. The problem is that some contractors
have taken things a step further,
and bring a cooler to the jobsite to store
spare battery packs. According to Goger,
keeping cordless battery packs cooler
than 50 degrees F is unnecessary, and
may be harmful. Says Goger, “Chilling
the battery can fool the charger into
thinking all the cells are cool when the
inner cells may still be warm.” He also
points out that the added risk of getting
water in the battery pack far outweighs
any marginal benefit.
While they should be protected from
extreme heat, NiCd batteries don’t need
to be babied. “A battery’s comfortable
working temperature is about the same
as your own,” Goger says. “When it gets
too hot for you to work, just remember
to bring your batteries in with you.”
Myth 3: Batteries can be rebuilt. Some
repair and electronic shops claim they
can rebuild battery packs so they will
perform as good as new. The problem
is you may get less than what you
thought you were paying for. “It’s
impossible to be certain that your local
electronic shop is rebuilding the pack to
the same specs as the original,” Goger
says. For example, not all cells are created
equal. “A rebuilt battery may perform
as good as new at first, but there’s no way
of knowing how well those cells will
accept a charge after a few dozen cycles.”
“Pros average about three years per
pack,” Goger says. “At that rate, even an
$80 pack costs less than 40 cents per
day.” He also points out that building
cost analysts have found battery powered
tools are not only more convenient,
but the batteries cost less than cumber-some
extension cords used to power
electric tools. And when a kink or cut
can turn a cord into a 120-volt jobsite
hazard, cordless tools are a better way to
provide extra safety and peace-of-mind.
About the Author
Joe Hurst-Wajszczuk has been writing
about woodworking and tool topics
for the past decade. He has appeared
in American Woodworker, This Old
House, Popular Woodworking, and
other publications. Additionally, he
has written and edited several books
with Rodale and Reader’s Digest. He
works from his home office/workshop
in Denver.
