The Apple //e has for the most part only functioned as boot off floppy disc where one disc may contain the operating system, and the other may have applications, and sometimes they boot directly into applications in questions. Floppy disks from that time frame that are functional at all are luck of the draw, as they are well beyond their known useful lifetime. Being magnetic, anything that comes near them that is magnetic from the old CRT screens that are typically connected to the Apple //e to the the keyboard itself while the computer is one can effectively demagnetize and render it useless. Obviously since the keyboard is right under where you typically stack the disk, as long as it is not sitting right on the keyboard you are fine.
I am not sure if the Apple // had a CMOS battery. Usually it either is a coin battery or 1/2 AA battery. A few of them the Apple batteries were box shaped and sat on velcro attachments on the logicboard on some computers. Look inside, but don't touch unless you are accustomed to removing static electricity using the power supply of the computer. Never touch with both hands!