The usual aneroid or mercury barometer does not have a battery so will not need changing.

How do you tell if a barometer is working?

Hold the instrument at the 45-degree angle and check the the level of the mercury in the glass tube with a long "stick" barometer. If the barometer is working correctly, the mercury inside will rise quickly to fill the very tip of the tube, leaving no air bubble.

Why would a barometer stopped working?

Ensure your barometer is broken. Non-mercury barometers should always be read as if at sea level. ... Check the adjusting or transporting screw at the base of the barometer. If it is screwed too tightly the adjusting screw will prevent the mercury from falling when pressure falls, and only works when pressure increases.