As I said, if the charity is willing to place a value, that usually is a good thing (especially if it's a specialized charity that knows what these devices are worth). The IRS has enjoined the charities of late (especially car donation ones) from inflating the market value over what it's practically worth. Your reputable charities will know this.
Ldij's numbers come right out of the posterior. You're joking if you think there's a 10% residual value on these things Declaring a used personal item at $1000-1500 is going to require justification (an appraisal of some sort).
The fuller explanation is in Pub 526
https://www.irs.gov/pub/irs-pdf/p526.pdf
I didn't pull the five year deprecation out of my ass, see:
http://www.centuryhearingaids.com/blog/donate-your-hearing-aids-tax-deduction-tip
or here (specific to Starkey's even):
http://www.mcguireshearing.com/pages/donate.php