Compare the cost of different kinds of cells and how long they last in a circuit. Decide which cell would be the most economical to use.

Design a way to test the D-cell battery while the flashlight is operating. Record the voltage change of the D-cell until it is depleted. Study the graph of the discharging battery.

Recharge a depleted rechargeable battery. Test its voltage before and after the charge. Did the battery return to its labeled voltage?