LEAD-ACID BATTERIES have been around for over 170 years now –
ever since Gaston Plante built the first one back in 1834. They are used in huge
numbers all around the world, mainly in the automotive industry. There’s at
least one in virtually every car, truck and bus to start the engine and power
ancillary equipment, while multiple lead-acid batteries are also used in many
electric vehicles to provide the motive power.
They’re also used in large numbers for energy storage in solar
and wind power plants. And by the way, we’re talking about "wet" or liquid
electrolyte batteries here (also called "flooded" lead-acid
The lead-sulphate effect
Although we’d now be lost without them, lead-acid batteries are
not without their faults. Probably their main drawback is that they have a
relatively short working life, typically no more than about three or four
Why is this? Well, every time energy is drawn from a lead-acid
battery, lead and sulphate ions from the electrolyte combine and are deposited
on the plates in the form of soft lead-sulphate crystals. Then when the battery
is recharged, these crystals dissolve again in the sulphuric acid
More accurately, MOST of them re-dissolve – but not all. Even
if the battery is never over-discharged and is always recharged promptly after
it has been discharged, a small proportion of the lead sulphate remains on the
plates. These then harden into "hard" lead-sulphate crystals which are much less
soluble and less conductive than before.
In practice, the formation of these hard lead-sulphate crystals
ually reduces the energy storage capacity of the battery. It does this
both by masking the active areas on the plates and also by reducing the
concentration of lead and sulphate ions in the electrolyte.
This "sulphation" effect has been understood for many years.
It’s also well known that the effect occurs much faster if a battery is
over-discharged, left in a discharged state for more than a few hours, or
frequently under charged. In fact, batteries mistreated in any of these ways
tend to have a very short working life indeed.
For a long time, sulphation was regarded as non-reversible and
batteries that had lost too much capacity due to this effect were simply
discarded. This was not only wasteful but was also an environmental problem,
because both lead and sulphuric acid are highly toxic materials.
Around the middle of last century, though, people in rural
areas discovered that they could "resuscitate" sulphated batteries by zapping
them with high-voltage pulses from their electric fence controllers. They didn’t
exactly understand why this method worked but kept using it because it did.
Subsequently, in 1976, the US Patent Office granted a patent to
William H. Clark of Salt Lake City, Utah, for a method of charging lead-acid
batteries by means of narrow high-current pulses. This was claimed to more
effectively dissolve the lead sulphate crystals and hence prolong battery life.
Since then a number of designs for pulse-type battery rejuvenators or "zappers"
have appeared in electronics magazines, including one published in SILICON
CHIP (Circuit Notebook) in February 2003 .