We need to remember that hearing aids are an electronic device. Moisture is very bad for electronics. The ear is a warm moist place. It is amazing that hearing aids work and last as long as they do.
Recent developments in nano coating has helped tremendously with keeping moisture out of the electronics of hearing aids.
Most people wear their hearing aids 12 to 16 hours per day. That equates to 4,320 – 5,760 hours a year. At some point the small components of the aid is going to wear out just like parts in a car. It is pretty normal to have to have a hearing aid repaired within three to five years or sooner if it is not kept clean and repaired when needed.