There will be no problem in charging your Kindle. I charge my Ipad and laptop and wife charges Kindle all the time on ships.
NAVIGATOR OF THE SEAS - 12/1/13
NAVIGATOR OF THE SEAS - 12/8/13
NAVIGATOR OF THE SEAS - 3/2/14
NAVIGATOR OF THE SEAS - 4/6/14
RADIANCE OF THE SEAS - 5/23/14
OASIS OF THE SEAS - 10/14/14
The only problem I have had with my nook onboard is that I don't get a chance to read it in public. There is always some nice passenger stopping to ask if I like having one - then the conversation starts :-)