I just had a tenant ask me if he could install a battery-powered ring doorbell to his unit (on his own dime).

I would not accept a dime from him.  

The side-by-sides are a dime a dozen but the stackable makes seem to be a bit harder to come by.

To put this in perspective, I think you have a less than 50% of ever seeing one dime from these people.

Tell the idiot to buy her own house and play hgtv on her own dime ! 

They waste a whole lot of your time and do not close the deal.They want possession of the property without putting a dime on the table (owner financing, I'll pay your mortgage (maybe) ...)They only want to resell it for a profit and sometimes with a rent to own buyer while you hold the title to the property and take on the liability while they collect a down payment and rent...and BTW, you were not paid a down, or rent...the investor gets 3 paydays, and you risk a trashed house, liability, eviction, everything with the hope you will sell the house in a few years.

No you cannot charge one dime additional.

And its true, you don't want to needlessly run off excellent, long-standing tenants because you want to squeeze an extra dime out of the place.

So, it's entirely possible your tenants will just go stay with friends, anyway, and they'd just be hoping to cash in or have a stay-cation on your dime.  

If it is damage that can be fixed with $300, I'd just plan to do it at move out on your dime.