多少Ω的電阻才適合替鎳氫電池放電？

It depends how LONG you would like your battery to be completely discharged.
The higher the resistance you use, the longer the time you have to wait before completely discharging the battery.

For example, if the voltage of the battery is 3.6 v (a typical mobile phone battery), the use a 100 ohms resistor would give the following results:

dicharging current = 3.6/100 A = 0.036 A or 36 mA
Suppose the battery is of capacity 1000 mA-h
then time needed to fully discharge the battery
= 1000/36 hr = 28 hours.

Be aware that the power dissipated in the 100 ohm resistor during discharging is = (0.036)^2 x 100 W = 0.13 W. Therefore, a 100-ohm, 0.5W resistor will be sufficient.

If you use a 56k-ohm resistor, the discharging time will become unreasonable long (15 000 hours, or 1.7 years). Its use is thus not appropriate.