NiCad batteries begin to leak after a few years. Servicing of the E-meter every few years is therefore required to avoid damage caused by leaking NiCad batteries, whether or not the E-meter is used.
After the batteries begin to leak they can quickly destroy copper tracks on the PCB [printed circuit board] on which they are mounted. At this stage avoid touching the batteries with your hands as the discharge is highly toxic. Washing hands after replacement is highly recommended.
The replacement batteries are the "tagged NiCad" type and can be purchased at any components store. If the tags on the new batteries are bigger than on the original batteries then it may be necessary to insert PCB pins and solder the batteries to the pins rather than trying to make them fit into the board by themselves. Also, if the batteries are left long enough to leak, this can cause the outer plastic sleeving on the batteries to shrink. If this happens, and the meter is given a hard enough knock, then the batteries run the risk of their cases shorting together. This could potentially cause smoke to come out of your E-meter!!!!
The E-meter should always be stored in its case with the case standing vertically. This ensures the needle of the E-meter dial is dangling downwards. The E-meter should never be stored flat on its back. If the E-meter is stored flat, the needle will slowly bend under gravity, suffer fatigue, and will over the years start to touch the dial face, ultimately causing the needle to stick. To remedy this stuck-needle phenomenon, lie the E-meter on it's face overnight so that the needle is bent by gravity away from the dial face.