all the advances that have been made in recent years in automotive
electronics, the lead-acid battery seems rather dated. The basic
chemistry inside a car battery has not changed, and average battery
life is still only about four to six years (and can be as little as
three years in really hot climates).
Batteries are also
temperature sensitive. The chemical reactions inside a battery that
produce current slow down as the temperature drops. Because of this, a
battery’s output can be reduced as much as 60 percent at zero degrees
F. Consequently, if the battery is undercharged to begin with, or not
in very good condition, it may not be able to deliver enough power to
crank and start the engine.
In spite of these shortcomings, there
have been steady improvements in lead-acid battery technology since the
earliest days of the automobile. Up until the late 1950s, most vehicles
operated on 6-volt electrical systems.
The switch to 12-volt
electrical systems was a major step forward because it allowed more
reliable cold weather cranking and starting, better lighting, more
powerful electric motors for wipers, power windows and seats, and the
use of more efficient alternators instead of generators to keep the
The old heavy black rubber battery cases that
were common up until the 1970s were replaced by thinner and lighter
plastic cases. Venting was also improved to reduce corrosion around the
battery terminals. In the 1970s, General Motors introduced the side
terminal battery, which reduced terminal corrosion even more. Other
improvements included thinner and more efficient cell plates and grids
that allowed more storage capacity to be packed into the same-sized
case or a smaller case.
One of the biggest improvements was the
introduction of “maintenance free” sealed top batteries. All batteries
produce hydrogen gas when charging. This is partially a function of the
metal alloys used in the battery grids. Reducing the amount of antimony
in the grid alloy, or replacing it with calcium or lead-strontium
reduces gassing so the battery uses less water over time. Less gassing
also reduces the risk of a battery explosion when jump-starting a
The Absorbed Glass Mat (AGM) battery was another major
innovation. In this design, the acid is held in sponge-like fiberglass
mats sandwiched between the positive and negative cell plates. This
almost eliminates evaporation and gassing, as well as the risk of
spillage. The AGM design also makes a battery more resistant to
vibration, which improves durability and reduces the risk of premature
Another innovation was to reconfigure the design of the
battery cell itself. Instead of using flat rectangular cell plates and
grids, some batteries feature a “spiral wound” cell construction that
packs a lot of surface area into a smaller volume. Combined with AGM
technology, it improves battery performance, durability and longevity.
typically fail for one of several reasons: chronic undercharging (which
causes plate sulfation, rapid aging and loss of charging and storage
capacity), vibration (which can crack separators and cell connectors
inside the battery), and loss of water (due to excessive temperatures,
evaporation or overcharging). Batteries can also freeze if they are
discharged and the temperature is below freezing.
A battery’s state of charge can be determined with a voltmeter. A fully charged battery should read about 12.68 volts.
reading of 12.45 volts indicates the battery is 75 percent charged.
Anything less means the battery is low and needs to be recharged.
a battery is low, the output of the charging system should be tested
with the engine running, and should be around 1.5 to 2.0 volts higher
than battery voltage.
Also, the battery cables and terminals
should be checked for tightness and corrosion, and cleaned if necessary
to restore a good electrical connection.