I have been attempting to load a battery discharge curve, but I can’t get it to work.
Basically, a fully charged led acid battery will have a voltage of 2.25 volts per cell so a six cell car battery will have a post to post voltage of 13.5 volts. A fully discharged one will have 1.70 volts per cell or 10.2 volts post to post. To discharge below that value is to risk permanent damage to the battery. As stated in the previous answer, it will only show that voltage right after removing the charger. It will drop to 2.20 volts per cell quite quickly but, the self discharge rate drops off with time and appears to very close to the same curve of a discharging capacitor through a very large resister.