Proper maintenance and care will extend the life of your hearing aid. Make it a habit to:

• Keep hearing aids away from heat and moisture.
• Clean hearing aids as instructed. Earwax and ear drainage can damage a hearing aid.
• Avoid using hairspray or other hair care products while wearing hearing aids.
• Turn off hearing aids when they are not in use.
• Replace dead batteries immediately.
• Keep replacement batteries and small aids away from children and pets.

Source: http://www.nidcd.nih.gov/health/hearing/hearingaid.htm#5