CHAPTER 7 ■ NINE-VOLT BATTERIESBattery Brand Names
Stiff competition has ensured that there’s no performance difference between most popular battery brands.
Instead of brand name, pay attention to battery chemistry (alkaline, NiMH, and so on), price, and freshness date.
Watch out for batteries with a voltage rated at less than 8.4 volts. For example, some NiMH rechargeable
9 V-size batteries are only 7.2 volts. The cause? Instead of seven internal cells, those batteries contain only six
cells and some filler (see Figure 7-16). Tsk. Tsk.
Figure 7-15. Tweaked alkaline 9 V batteries
Figure 7-16. Polystyrene foam filler in a less-powerful battery
Although a lower voltage is detrimental to many applications, it does provide a lower-weight and a
lower-power battery in a standard form factor (case style). For example, if your robot doesn’t need all
9 volts, substituting the lower-voltage battery can save some weight or slow down a robot that fails because
it operates too quickly.
Using 9 V Batteries in Robots
Generally speaking, the higher the voltage, the faster the motor’s speed and the greater the motor’s push.
The first time I set Sandwich down onto a track, I was disappointed in the robot’s line following. The
motors were too fast for sharp turns. So, I switched from a fresh 9.5 V alkaline battery to a 7.2 V rechargeable.
The lower voltage produced lower motor speed. The slower speed had a dramatically positive effect on the
line following.