automatic battery discharger
One way is to use a resistor which draws low enough current so that the discharge of a fully charged battery takes several hours. This way you can watch the terminal voltage with a VOM and stop it at 1.00 volts.
If you want to do it automatically, use a comparator to sense the 1.00 V and have a transistor on the low side of the resistor. The The transistor is connected to a flip flop to control the gate/base. The comparator flips the flip flop to the off state. Use a switch and resistor to flip it to the on state.
There are several automatic chargers/dischargers on the market that do this automatically, but they use fast charge and discharge which makes the battery hotter. This will reduce the number of charge/discharge cycles the battery will withstand.