The following circuit is a universal battery charger for Ni-CD batteries. Q1 can be replaced with any 1Amp rated NPN transistor. The LED will indicate battery is charging. R2 will determine the current and rate of charge (see the table below).
| R2 | CURRENT |
| 47 | 50mA |
| 18 | 100mA |
| 6.8 | 200mA |
| 3.9 (1/2 watt) | 300mA |
| 2.7 (1/2 watt) | 400mA |