tech41

The How of Batteries
by Lynn Bennett

How many times have you planned a ride on your British bike only to
find the battery so dead that the bike won't start? Or had the battery
boil over onto you polished cases, the frame, or the chrome pipes? Or
had the battery die during a long ride? Well, what makes these simple
looking devices work? How can we guard against some of these problems?

Batteries are energy storage devices. When charged up they store
energy, albeit in chemical form, to be used later. When we force
current through a battery backwards, that is raise the battery terminal
voltage above the battery's nominal 12 volts DC, we cause a chemical
change to the battery acid (or gel or whatever chemically impregnated
mat used). That change in a lead acid battery (the most common kind
used in cars and motorcycles) can be measured by the specific gravity
of the battery acid. Before sealed batteries hydrometers were common
devices used to measure specific gravity. You would draw a small
quantity of battery acid from each cell, and observe the reading or the
number of "balls" floating. This was done individually on each cell.
Often times only one cell was low or would not take a charge. Modern
sealed batteries can be measured for charge by the terminal voltage,
which raises insignificantly but measurably during the charge cycle. At
a later time the chemical reaction can be reversed and a current can be
supplied by the battery, releasing the battery's stored energy.

Batteries are rated and sized by their storage capacity in ampere-hours
(amp-hour). That is a product of a continuous current drain for a
period of time: high current for a short interval or a low current for
a long time. For example, a 9 amp-hour battery can supply 9 amps for
one hour or 1 amp for 9 hours. That's the theory, at least. Heavy
current drains can damage a battery when the resultant internal heat
warps the battery plates.

Today there are several types of batteries but only three basic types
available for motorcycles: un-sealed, sealed liquid acid, and sealed
gel acid. Un-sealed batteries have removable caps and can be tested
with a hydrometer. They also have vent tubes to allow the hydrogen gas,
produced in the re-charge cycle, to escape. Those same vent tubes can
allow the battery acid to leak out and spill onto the bike. Sealed
liquid acid batteries have battery acid like the un-sealed versions but
have a chemical additive that limits the need for continuous venting.
The venting only occurs in catastrophic conditions rarely if even seen
in everyday use (high internal pressure). Sealed batteries can be
tipped over without leaking acid which makes them ideal for off road
crash prone motorcycles. Gel cells are also sealed units but use a gel
or paste instead of a liquid acid. They have all the advantages of a
liquid sealed battery except they can be two times more expensive. It
should be noted that sealed batteries tend to cost two times what an
un-sealed one costs. I believe all British bikes (or all bikes for that
matter) should use sealed batteries to reduce the chance of a battery
venting acid onto our beautifully restored masterpieces. When asked I
would recommend the use of the Yuasa YTX9-BS or equivalent for
non-electric start British bikes. It is smaller than the normally
specified Brit unit but can made to fit in most Brit bike battery boxes
and is more than adequate for our uses.

What makes a battery "boil" over? Overcharging! If your bikes charging
system ever raises the battery's terminal voltage above about 14.5
volts DC the battery is being destroyed by overcharging. That means at
any engine RPM! What makes a battery loose its' charged state? Drawing
current out of it and not putting it back in! If your bike's charging
system does not make the battery's terminal voltage at least 13.5 volts
DC by about 3000 RPM your battery will eventually be drained by the
lights and ignition system and go dead. So keep your charging system up
to snuff. What about the times you don't use your bike? The battery
will slowly loose charge on its' own. So keep it on a battery
maintainer that charges it first, then trickles a milliamp charge into
it automatically. Regular battery chargers normally will overcharge a
battery if left on them. Only the special battery maintainers (like the
Battery Tender) protect the battery.

This brings me to a story. A friend delivered to me a new battery he
just picked up for a project bike I was working on. He indicated that
the salesman said that it was fully charged even though the acid had
just been added, How could that be true? When I put it on an automatic
charger it immediately indicated a fully charged state. How can that be
with fresh acid? The acid had been removed after recharging of the
battery and the charge remained with the acid in chemical form and in
the battery's plates. Separating them had not effected the charge state
of the battery. Most batteries are shipped to a retailer without the
batter acid in the battery. This is mostly due to hazardous materials
shipping regulations but when shipped dry like this they have a
substantially longer shelf life. They can be called to service by
simply adding the acid.

Take care of your battery and make sure your bike's charging system is
100% OK. And use the sealed batteries to avoid damaging the finish of
your beautiful vintage machine. Have a safe and fun vintage ride.