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Garage Day:
How to Determine If Your Battery is Dead
S t u O l t m a n • S e n i o r T e c h n i c a l E d i t o r
orry, Doc, but your patient is dead.” Remember those old B movies An emergency room staff, garbed in
“Sghostly white gowns and masks would solemnly deliver the bad news. Cue the violins…
But just how do you know your Gold
Wing’s battery is really ready for eternal rest
What if the headlight comes on Is there still
power in the old wet cell What if the starter
motor spins and the engine starts the moment
you release the starter button Is the gel cell
still gellin’ What if the starter gives a grunt or
two, followed by a few clicks from down in the
bowels of the bike, then silence Was that
grunt good news or bad
And even if you’ve faithfully kept your
bike’s battery on a multi-stage maintainer, you
can’t expect a battery to last forever. Someday,
sure as you’re born, your bike will exhibit
some of those nasty symptoms just
described—and you can almost guarantee
your battery is toast, fried, drained, exhausted.
If you’re still using a wet cell battery, the
best way to determine if it has any charge left
in it is with a hydrometer. Open the cells and
extract enough fluid to float the little indicator
inside the hydrometer’s tube. Like as not,
you’ll find the float doesn’t.
But how do you measure the battery’s
health if it’s a sealed cell battery
We asked Senior Technical Editor Stu
Oltman to show us how.
With the battery extracted from the bike
and resting on his workbench (more for photographic
convenience than for necessity), he
connected a multimeter and a load tester to
the old YUASA AGM battery.The battery had
been OEM equipment from a Gold Wing but
had been unused for months. Despite that, it
had been on a maintainer steadily.
As seen in Photo A, the voltage across the
battery terminals is 12.75, so the battery may
be okay. And many a motorcyclist has been
deceived by this surface charge.
When a load is put on the battery, as Stu
does with the load tester, the voltage falls rapidly
to 10.02 volts, indicating the battery no
longer has adequate cold cranking amperage
to both provide spark and to run the starter
motor simultaneously.
A
Photo B shows Stu’s load tester, with voltage
readings across the top of the gauge (14,
12, 10 volts, etc.). Before Stu applies a load to
the battery, the gauge shows a good reading in
the green zone. But as soon as he puts a load
on the battery, the reading drops off instantly
into the red zone (Photo C). Seen clearly in
Photo D, the battery’s voltage has now
dropped to 10.02 volts—likely inadequate to
start the bike.
Stu explains, “It takes twice as much current
as my load tester draws to actually get
the engine spinning.The starter motor draws
100 amps after the engine cranking speed stabilizes,
but up to 200 amps may flow the
instant the start button is pressed. So when
you hit your starter button, the voltage of this
particular battery would drop down to even
less than 10 volts—not enough. But when you
release the starter button and the load from
the starter motor is gone, the voltage instantly
spikes back to 12 volts or more. So if the
engine is still spinning at that instant, the spark
plugs may fire and the bike will start.”
Knowing this is the case, a wise owner will
understand what’s happening and replace his
battery before it fails completely—say, the
next time he tries to start the engine.
What’s with that little clicking sound
That’s the starter solenoid. It’s an electric
switch used to control a large amount of electrical
current with a much smaller amount.
Rather than needing to run a huge cable from
the battery to the starter switch, then to the
electric starter, a solenoid allows motorcycle
manufacturers to run a couple of thin wires
from the starter switch to the solenoid. Push
the starter button, and a tiny bit of current
from the start switch creates a magnetic field
that pulls a little piston into place, closing the
direct current circuit from the battery to the
starter motor (that does have heavy gauge
wire connecting them).
If your battery is weak, the clicking you
hear is the solenoid trying to stay engaged but
repeatedly failing due to dropping voltage. Like
a fluttering heartbeat, it’s a symptom that your
patient is in trouble. As we said, cue the violins.The
patient is dead.
●
B
C
D
May 2007 43