Turn off the device and remove the battery if possible
Inspect the battery for swelling, leaks, corrosion, or damage
Check the battery label for voltage and chemistry
Set a multimeter to DC voltage
Place the red probe on the positive terminal
Place the black probe on the negative terminal
Compare the measured voltage to the rated voltage
Test under load if possible
Use a battery tester for the correct battery type
Check whether the battery holds charge over time
Replace the battery if it fails voltage or load tests