As a business, it is your prerogative to set the security deposit at whichever amount you see fit.
However, it is a common and recommended practice to set the security deposit at the same amount as your insurance deductible.
Wheelbase's insurance deductible is 2% of the value of the vehicle, with a
Minimum of $500 and a Maximum of $1,500.
If the unit were damaged and needing an insurance claim, you would have the deductible amount already from the renter and not have to chase them down for it.