Virtually all the cruise ship lines have either always had a policy against scooters or wheelchairs in the hallways, or have recently changed their policy. It is a fire hazard, and for those who use a wheelchair full time, your scooter blocks our way in the halls. If you need a mobility device, then you need to get an accessible cabin that will accomodate your equipment needs. You can ask if they have a non-hallway area near your cabin where you can store and charge your scooter...someone may have to go get it for you in the AM. Some ships can accomodate this.
Monarach of the Seas is now considered an old ship, and older ships are less accessible with fewer accessible cabins. It is common to have to book accessible cabins 9-12 months in advance.
Some ships have pool lifts. Look at RCL's newer ships, and some of the newer Princess ships. Otherwise most are totally non-accessible unless someone can pick you up in their arms and lift you in and out of the pool.