Could have a battery drain, Battery could just be old, Could be many things.
You will get a voltage drop when you go to crank the car, Hence the dash lights going out. (Battery only has a surface charge that gets wiped out when you draw excess current to try crank the motor over).
Charge the battery, Get the car running and then see if the car is charging to battery by using a multimeter. If you can get a hydrometer check the acidity of the battery is consistant across all cells..