Mercury is used as a stabiliser which helps give batteries a longer shelf life.
Fortunately the average content of mercury in zinc-air hearing aid batteries is less than 1 per cent. This is significantly less than the early generations of mercury-oxide hearing aid batteries during the 1970s which had a mercury content of up to 50 percent!
Mercury is a naturally occurring liquid metal which, in large amounts, is hazardous to our planet and to people. If we all work together to choose very low or mercury free batteries, the reduction in mercury use world-wide will be significant and a good choice for our environment.
We will start to see mercury-free batteries become a standard offering from mid-2011 due to an EU ban on products containing mercury. A similar ban comes into effect in two states in the USA on 1 July 2012.