88 Deville Fuel Issue

My car wouldn't start. I charged the battery, and it started, only the fuel gauge shows that my car has 6 gallons of gas (18 Gallon tank), but is on L miles for the range. Its only shown low when I'm out of gas. Is there a problem with a fuel pump or sending unit or (hopefully) something less expensive?

It lost its memory when the battery died. Just drive it a bit and it will adjust itself. Happens on my '93 sometimes if I have the battery disconnected for a while when doing yet another repair.