There is another set of rules that takes priority over the appraisal rules. This is important. I should have paid more attention when you said the power chair was paid for by insurance.
If you owned the chair less than 1 year, your maximum donation value is what you paid for it, regardless of its actual value. For example, if you paid a $500 co-pay, the value of your donation is $500. If you paid nothing, the value of your tax deduction is zero.
If you owned the chair more than 1 year, and you donated it to a charity that will sell it for fundraising, your maximum donation value is also only what you paid for the chair.
If you owned the chair more than 1 year, and you donated to a charity that will use it as a power wheel chair to help other people with mobility problems, then you can claim the fair market value. (The charity might donate it to a needy handicapped person, or maybe you donated it to a church that will use it when handicapped people need assistance to attend Sunday services, etc.). However even here, you can't claim a value over $5000 without a signed appraisal, and the charity must complete IRS Form 8282 and send it to the IRS to verify the donation.
These rules are in publication 526, https://www.irs.gov/pub/irs-pdf/p526.pdf
