5.0 Batteries
Batteries should be changed every four weeks or less. Alkaline batteries work well. Buy twice as many battery cartridges as needed so that when it comes time to change batteries you can bring a fresh set of full cartridges, rather than trying to put new batteries into the cartridges at sea. Colour-code the fresh cartridges -- it's too easy to mix them up when changing them during the haul-back. Try to minimise the time that the pinger insides are exposed to the elements.