I have a SFH that has been rented for about 2 years. The home came with a portable dehumidifier for the basement. Tenant contacted me today and indicated it no longer works. The basement is not wet, but of course does get humid.

Should I be obligated to replace, considering it's not apart of the house, nor is it an absolute necessity?  

What would you do?

Thank you

Replace it. They are not expensive, but could save you a tons of money if you start having moisture issues.

If your tenant is paying the $10-35/month (depending on size) to run the thing, I'd happily replace it.  Not only does it make the property more comfortable for them, but it protects you in the long term.