How to Test a Battery

CHAPTER 10: Mending and Breaking Electronics 239

Figure 10-3 Testing a fuse with a multimeter

(look for wires that have come lose, or any sign of charring), then try replacing the fuse.

If the fuse immediately blows again, don’t try another. You should instead find the source of the problem.

How to Test a Battery

Figure 10-4 Testing a battery using a resistor and multimeter Spent batteries are, of course, another common reason for something not working. Simply measuring the voltage will tell you very quickly if the battery is empty. During testing, if a 1.5V battery like an AA or AAA is showing less than 1.2V, or a 9V battery is showing less than 8V, it is probably time to throw it away. However, the voltage of a battery shown when it is not powering anything can be a little misleading. For a more accurate picture, use a 100Ω resistor as a “dummy” load. Figure 10-4 shows a resistor and multimeter being used to assess the state of the battery.