Power issue -

Hey there

Got a new MacBook Air last weekend and I've noticed something really strange. Sitting with the A/C adapator plugged in I have noticed that when I open my laptop it can be showing less then 100% charged or as I use it I have noticed sometimes *not always* while it is still plugged in the battery will start going down down down attempted to reset the SMC with apple tech online however he didn't mention it needed to be unplugged to do that so have no idea how effective that was so might need to try that again

Also sometimes I've noticed before I when I first wake it up before I log in it can be showing less than 100% but then once I log in it's up to 100% Odd anyone have any ideas ?