Lesson 2/Learning Event 1
VOLTAGE AND CAPACITY
There is a distinct difference between the voltage and capacity of a battery.
This difference can be easily seen by picturing two cans of water, one small and the other large,
placed on top of a building. If the water from both cans is poured over the side of the building,
the pressure or force it has when it hits the ground will depend on the distance it falls. The
distance is the same regardless of which can the water comes from. This is comparable to battery
voltage since voltage is electrical pressure. Each cell of an automotive battery has slightly over 2
volts. This is true regardless of the size of the cell.
Now, let's imagine that one of the cans contains one gallon of water and the other can five gallons.
You can see that if the water is poured from both cans at the same rate, water can be poured five
times as long from the large can. From another viewpoint, if we empty both cans in the same
length of time, the large can pours five times as much water in the same amount of time. This is
comparable to battery capacity. More battery capacity is obtained by giving the electrolyte more
plate surface to contact. This can be done by making the plates larger or by using a larger number
Battery voltage and capacity are different, and each one has a definite effect upon the other as well
as the circuit.
We know that the battery must supply the correct amount of voltage to push just the right amount
of current through the circuits. Too much voltage will cause too much current to flow, which will
burn out bulbs, and so forth. If battery voltage is too low, the current flow will not be enough and
the circuits will not operate right.
When a load is connected to the battery, the current flow will cause the battery voltage to drop due
to internal resistance in the battery cells. The amount of voltage drop under a load is affected by
The larger the capacity of the battery, the less the voltage drops.
As the battery's state of charge gets lower, the more the voltage drops.
The greater the current flow, the greater the voltage drop.