Charging circuit for bulk 1.2v 1200mah ni-cad batteries
If you're going to charge a string of cells with a constant current, they must be wired in series and you must provide a bulk supply with enough output voltage to supply the headroom and the reference for the regulator, as shown in this excerpt from TI's LM317 data sheet:



For charging current limits check the NiCd manufacturer's data sheet.

The power dissipated by the series resistor will be\$ 1.25V \times Ichg\$, and the power dissipated by the LM317 will be \$ (Vin - (Vbat + Vref)) \times (Ichg + Iref)\$.

Note that the LM317 will dissipate more and more power as fewer and fewer cells are connected.