At what voltage is a deep cycle battery dead?

They are rated to a final point of 10.5 volts. Until then, the lights become blurred and the image of the television is small. A specific gravity of about 1,200 or a voltage of 12.25 to 12.3 means that the battery is about 50 unloaded.They're rated at an end point of 10. The TV picture is small and the lights are dim. 50% of the battery is discharged if the Specific Gravity is between 1.200 and 12.3. It's almost dead by the time it's down to 12 volts.