Nickel metal hydride (NiMH) batteries produce 1.2 volts, when fully charged, the same as nickel cadmium (NiCd) batteries. During use, the battery gradually produces less and less energy until ultimately it doesn't operate your equipment; you often get very little warning that the battery is about to die. However, if you use a multimeter to occasionally test the charge level of your NiMH battery, you get advance warning of the energy level and can recharge the battery at a time that's convenient, rather than when you find that it's dead.
Turn on the multimeter. Set it to read volts so you can test the charge level of your NiMH battery.
Place the metal prong on the end of the black wire from the meter onto the flat base of the NiMH battery you want to test. Place the metal prong on the end of the red wire from the meter onto the top raised terminal of the NiMH battery.
Check the multimeter display. It should read 1.2 volts if the NiMH battery is fully charged. If the reading is about 1 volt the battery is probably about half empty; NiMH batteries can maintain their top voltage level for some time. If the reading is less than 1 volt you need to consider recharging it.