my note 3 is not hot until i put in the external storage card. what is wrong ?

is my ext storage card faulty ? the battery then start going downhill............
How big is the storage card? When you first put it in, if it has a lot of content, Android will take a while to index everything in the card. In the meantime, expect your phone to work overtime doing that, so battery life will take a hit until it finishes. This normally isn't a problem, but it becomes a problem if your card isn't inserted properly, or when the contact is loose, so the card repeatedly connects and disconnects. Every time that happens, Android has to re-index everything, so if this happens often, the phone will heat up and battery life will suck.
The S3 had this problem with certain Sandisk sd cards because those cards were slightly thinner than usual.