Battery drain down overnight
Sure,this is common on old stuff, and is usually a dead short somewhere, draining your battery. Anything that stays on, like a clock or an electric fuel pump, some lights left on, or even some corrosion on a socket that allows currrent to pass. If you have an alternator, get it checked. If it is shorted, it will pull a battery down in no time. Another thing is the starter solinoid. If it does not dis-engage all the way, it will do the number on you too. An electrical shop can test this for you, but my best way is to just remove one fuse at a time until the battery does not show a draw. you will need a meter for this. good luck.