Was given key fob with uncut key

I purchased a used car a few months back and recently have been having battery issues with it. If I don’t drive the car for a day the battery drains and the car won’t start. It’s a push button start so I never checked the manual key when I first bought the car but I figured I better make sure it works in case I can’t get the doors to unlock with my fob. Well when I pulled out the key it’s uncut and won’t work, I was only given the one fob so I haven’t been locking my car because I have no way to unlock it when the battery dies. Is this something that the dealer needs to fix or am I just out of pocket having to buy a new key that actually works for my door lock?