battery is fully charged is
by means of the voltmeter, as the volts slowly rise to the proper
point during the process of charging. A third way, and probably the
most reliable is by the use of the hydrometer. The voltage of each
cell when fully charged should be 2.5; it should never be discharged
below 1.75 volts. Many storage battery electric light plants on the
market are provided with a simple and inexpensive circuit breaker,
which automatically cuts off the current and stops the engine when the
battery is charged. The current is then thrown from the dynamo to the
house service by an automatic switch. If such a circuit breaker is not
included, it is necessary to throw the switch by hand when charging is
begun or ended.

Since the principal item of first cost, as well as depreciation, in a
storage battery electric light plant is the storage battery itself,
the smallest battery commensurate with needs is selected. Since the
amount of current stored by these batteries is relatively small,
electric irons and heating devices such as may be used freely on a
direct-connected plant without a battery, are rather expensive
luxuries. For instance, an electric iron drawing 400 watts an hour
while in use, requires as much energy as 20 tungsten lamps of 16
candlepower each burning for the same length of time. Its rate of
current consumption would be over 13 amperes, at 30 volts; which would
require a larger battery than needed for light in the average farm
home.

The use to which electricity from a storage battery is put, however,
is wholly a matter of expense involved; and if one is willing to pay
for these rather expensive luxuries, there is no reason why he should
not have them. Heating, in any form, by electricity, requires a large
amount of current proportionally. As a matter of fact, there is less
heat to be had in thermal units from a horsepower-hour of electricity
than from three ounces of coal. When one is generating current from
water-power, or even direct from gasoline or oil, this is not an
argument against electric heating devices. But it becomes a very
serious consideration when one is installing a storage battery as the
source of current, because of the high initial cost, and depreciation
of such a battery.

Farmers who limit the use of their storage battery plants to lighting
will get the best service.

_Portable Batteries_

Abroad it is becoming quite common for power companies to deliver
storage batteri