Try a dry n store dehumidifier or place hearing aids in a jar of dry rice. If moisture is coming from perspiration consider talking to hearing specialist about the style of device. In the ear styles usually have a vent, if you wear in the ears it may be perspiration, make sure it is not drainage from an ear infection. If you wear behind the ears you may be able to find a cloth covering specially designed to keep body of aid dry. Newer hearing aids have special coatings built in to the hearing device to prevent issues with moisture.

First you should probably keep your hearing aid and battery away from water.I suggest taking it out while in the shower/bath and cover your head with a hood or umbrella while out on a rainy day.If battery keeps shutting down then replace the old battery with a new one.If problem keeps accorring then maybe its time to take your hearing aid into your local hearing aid repair and let them solve the whole issue with why it keeps shutting down