MWD (Measurement While Drilling) batteries are used to power these downhole instruments. They are specially designed to operate in harsh downhole environments, including high temperature and high pressure. MWD batteries are critical components in the MWD system, as they must provide reliable and consistent power to the instruments for extended periods of time. MWD batteries typically use nickel-cadmium (NiCad) or lithium-ion (Li-ion) technology and are designed to have a long shelf life and to withstand high shock and vibration.