I would NOT recommend a power chair or scooter for shore excursions outside of the USA or Canada. You will not find shore transportation with a lift in most places. You cannot easily get them into small cabs. And most of all, many cruise lines will NOT tender a power chair. In addition curb cuts and ramps are far and few between ashore. You can use a power chair or scooter on the ship, but bring a manual chair and someone in your party who can push it when going ashore.
I travel with my parents just for this reason...my mother uses a power chair full time at home, but we have a van with a lift. On cruises, with help, using the manual chair we can get up and down stairs and in and out of cabs and see what we want to see even if there are no accessible tours (very rare).
In addition, power chairs and scooters can breakdown. A manual chair is a good back-up. When we get on the ship, my dad takes the manual chair piled with our carry-ons, my mother drives her power chair, and I bring up the rear with our travel lift.