Well it should not be doing that it would be something to do with:
A. The Portal Of Power
B. The Skylanders Swap Force/Giants/Spyro's Adventure Disk
C. The Skylander toy may have something wrong inside
D. The Games Information
E. The Game may be acting up
F. The Console your playing on
G. The toys info
If you have any other questions ask your locale retailer where you got the Skylanders and tell them your problem and then tell you to give them to them and get refund or get new Characters.
I am also having the same issues, after a few minutes of play, it says that the character is tired and needs rest. We have 8 swap force characters and he needs to switch them out every 2-3 minutes. Cord extended and the portal is not near any other devices. Does that mean that all the characters are malfunctioning?