I think a dryer is as good preventative measure. I have noticed that if I change the battery during the day, or open the battery drawer when going to bed in the evening, I can see some glistening of moisture on the battery drawer. Hearing aids have a moisture rating, but I am uncomfortable depending on that rating alone to ensure long term reliability against moisture damage. I live in a dry climate, but the moisture is still there, so it concerns me.
I did a quick check on dryers and found a good rating on a very simple device called Hal-Hen Super Dri-Aid product. It is just a jar of activated alumina and a few blue silica gel beads to indicate the condition of the activated alumina. Activated alumina in industrial applications is used to reduce the dewpoint of air down to the -40 range. So all I think it does is maintain a very low dew point air condition in the jar. There is no power required, and when it does require regeneration you do that in an oven or microwave.
And to seal the deal, when I walked into Costco they had the product for $20 (Canada). Probably is about $15 in the US if they stock it there. For me this is a perfect solution as we camp and don’t always have power, and there is always the hassle of finding a power outlet. Simple and foolproof. I recommend it.