Put it in Airplane mode and turn down the brightness while charging. See if it will charge to 100%. If not then take it back to the store and have them run a test.
How old is the phone? I'm pretty sure your battery is fine, the reading may just be off. Do you usually do a full cycle charge (0-1% to 100%)? Try that for a few days to see if the reading is calibrated.
oh snap I just remembered that happened to me too. I let it charge in the wall overnight. When I went to disconnect it said 98%. So I turned it off/on and it said 100%. That was earlier this month. So far so good I haven't seen it do that in awhile.
How old is the phone? I'm pretty sure your battery is fine, the reading may just be off. Do you usually do a full cycle charge (0-1% to 100%)? Try that for a few days to see if the reading is calibrated.