Yes it is a RES. Put him a ten gallon setup for a while and see how he does before introducing him to the larger tank. How big is your painted turtle. If it is alot larger than this little guy you might want to wait for him to put a little size on.
If so than try to get him into a larger tank than a 10 gallon. At his current size he should be fine in ten gallons but with proper care and feeding he is going to grow rapidly.
If he was in very shallow water for that long a period of time be sure to gradually raise his water level and monitor how he is swimming. Babies can handle deep water right from birth but if they are not allowed to swim and are only kept in an inch or so of water for a long period of time they need sort of "learn" how to swim as they have not had the experience yet.
Steve