ffectually,
although a plate of glass is generally laid over part of the top of
the jar, and that dirt and dust may fall into the jar.

Size. The capacity of storage battery cells is rated in ampere hours,
while power consumed by lights, motors, etc., is measured in watt
hours, or kilowatt hours. However, the ampere hour capacity of a
battery can be changed to watt hours since watt hours is equal to

Watt hours = ampere hours multiplied by the volts

If we have a 16 cell battery, each cell of which is an 80 ampere hour
cell, the ampere hour capacity of the entire battery will be 80, the
same as that of one of its cells, since the cells are all in series
and the same current passes through all cells. The watt hour capacity
of the battery will be 32 times 80, or 2560. The ampere hour capacity
is computed for the 8 hour rate, that is, the current is drawn from
the battery continuously for 8 hours, and at the end of that time the
battery is discharged. If the current is not drawn from the battery
continuously for 8 hours, but is used for shorter intervals
intermittently, the ampere hour capacity of the battery will be
somewhat greater. It seldom occurs that in any installation the
battery is used continuously for eight hours at a rate which will
discharge it in that time, and hence a greater capacity is obtained
from the battery. Some manufacturers do not rate their batteries at
the 8 hour continuous discharge rate but use the intermittent rate,
thus rating a battery 30 to 40 percent higher. Rated in this way, a
battery of 16 cells rated at 80 ampere hours at the 8 hour rate would
be rated at 112 ampere hours, or 3584 watt hours.

In determining the size of the battery required, estimate as nearly as
possible how many lamps, motors, and heaters, etc., will be used.
Compute the watts (volts X amperes), required by each. Estimate how
long each appliance will be used each day, and thus obtain the total
watt hours used per day. Multiply this by 7 to get the watt hours per
week. The total watt hours required in one week should not be equal to
more than twice the watt hour capacity of the battery (ampere hours
multiplied by the total battery voltage) at the eight hour rate. This
means that the battery should not require a charge oftener than two
times a week.

The capacity of a battery is often measured in the number of lamps it
will burn brightly for eight hours. The watts consumed by motors,
heaters, etc., may be expre