CHAPTER 7
Nine-Volt Batteries
Sandwich, the line-following robot, uses a 9 V battery for power. In fact, most of my robots use 9 V batteries
because the batteries are so small and lightweight. In this chapter, you’re going to learn how to test a 9 V
battery (see Figure 7-1) and find out about the differences in battery brands and chemistries.
Figure 7-1. Alkaline 9 V battery
How many volts in a nine-volt battery? Yes, it’s sort of a trick question. Although the answer is
somewhere around nine volts, the actual voltage varies based on what the battery is made of and how much
of the battery’s power has been used up.
During this stage, it’s not necessary to understand exactly what “voltage” is. However, if you’d like, you
can think of voltage as water pressure coming out of a water pump. A pump with more pressure can spray
water harder than a pump with less pressure. Likewise, a battery with more voltage can spray electricity
harder than a battery with less voltage.
The unit for voltage is volts or simply the letter V. So, 9 volts and 9 V mean the same thing.