What size battery is needed?
A battery should be big enough to allow reliable
cold starting. The standard recommendation is a battery
with at least one Cold Cranking Amp (CCA)
for every cubic inch of engine displacement (two for diesels). CCA rating
is an indication of a battery's ability to deliver a sustained amp output
at a specified temperature.
Specifically, it is how many amps a new,
fully-charged battery can deliver at 0 degrees F for 30 seconds and
still maintain a minimum voltage of 1.2 volts per cell.
A rule of thumb says a vehicle's battery
should have a CCA rating equal to or greater than engine displacement
in cubic inches. A battery with a 280 CCA rating would be more than
adequate for a 135 cubic inch four-cylinder engine, but not big enough
for a 350 cubic inch V-8.
Battery manufacturers have been trying to
outdo one another by introducing batteries with higher and higher cold
cranking amp ratings. There was a time when a battery with a 550 CCA
rating was considered a powerful battery. Now there are batteries with
650, 750, 850, and even up to 1,000 CCA available.
One reason for the "amp wars" between
battery manufacturers is that bigger is definitely better. How much
overkill is really necessary to assure reliable cold weather starting?
Two amps per cubic inch of engine displacement? Three, four or five
amps? The bottom line is bigger sells better.
The difference between a group 23 battery
and a group 24 battery is 1/2" in length, 1/16" in width and
7/16" in height. It does not sound like much, but it is enough
of a difference that the longer battery might not fit the space provided
for the shorter battery if a swap were attempted.
Since there is little or no effort on the
part of vehicle manufacturers to standardize original equipment battery
dimensions, aftermarket battery suppliers are faced with the task of
trying to cram as many amps as they can into the smallest battery case
that will fit the most applications.
Consolidation reduces the number of different
batteries a jobber has to stock to cover the various vehicle applications.
It also simplifies manufacturing by building fewer basic battery sizes.
The most powerful battery in the world will
not be able to do its job properly if battery cables are not up to the
job. One often overlooked source of cranking trouble is undersized battery
cables. If the original equipment cables have been replaced with cheap
ones with undersized wires, the cables may not be able to deliver the
battery's full amp load to the starter.