The life of the average dry cell is about twenty ampere hours under normal conditions. If however the cell is discharged at a high rate, say for instance, five amperes, it will be found that the life is less than twenty ampere hours. On the other hand, if the discharge rate is very low, as for example, one-quarter of an ampere, the capacity of the cell will be greater. In order to get the most economical service from a battery it is therefore advisable to lighten the load as far as possible, and cells are consequently often connected in *series-multiple* with that result in view. In a case, for illustration, where it might be desirable to secure a current 4 1/2 volts and five amperes from dry cells, the series-multiple arrangement could be recommended. Three dry cells connected in series will furnish 4 1/2 volts and five amperes, but by using two sets as in Figure 35, the load is divided between them and each set will only have to furnish amperes to the circuit. *Two sets of cells used in series-multiple will therefore last more than twice as long as either set would alone.* The series-multiple arrangement is recommended where cells are to be used for operating toy trains, induction coils, motors, etc., as being the most economical. Always be sure to use large wire in connecting cells. Fine wire offers considerable resistance to the electrical current and the full benefit of the batteries cannot be secured when it is used. [Illustration: FIG. 35.—Showing how to connect a Battery of Cells in Series-Multiple.] Use care to scrape all connections so that they are clean and bright. Tighten the binding posts with a pair of pliers so that there is no chance of their becoming loose. Another wise precaution is to always arrange batteries so that there is a small space between two cells and no likelihood of any of the wires or binding posts coming into contact with one another so as to form a short circuit. After the connections have been carefully made a little vaseline smeared over them will prevent corrosion. [Illustration: FIG. 36.—Battery Connectors like that shown above can be obtained for 1 1/2 cents each and will be found to be very handy.] Storage or Secondary Cells. Storage or secondary cells (also sometimes called accumulators), differs from primary cells in that they will not give forth an electric current until they have been *charged* by passing an electric current through them. [Illustration: FIG. 37.—A Simple Experimental Storage Battery consisting of two Lead Plates immersed in Dilute Sulphuric Acid.] The Storage Cell is therefore a very convenient means of taking electric energy at one time or place and storing it up for future use. From this it must not be implied that electricity is actually stored in such a battery. The energy of the electric current is really changed into chemical energy and this energy produces electricity when the cell is again discharged.