The following diagram is the schematic diagram of Ni-CAD battery charger circuit which featured with current and voltage limiting to keep the battery lifetime.
The lamp L1 will be light brightly and the LED will be out when the battery is low and battery charging in progress, but the LED is very bright and the lamp L1 dim when the battery is almost ready to use (charge complete). L1 must be a bulb lamp rated for the current you want (usually the battery capacity divided by 10).
The diode D1 should be at least 1 A, and Z1 is a zener diode 1 W with a voltage determined by the fill-charge battery voltage minus 1.5 V. When the battery is fully charged, the circulatory flow around the battery capacity divided by 100 mA.
The supply voltage can be from 12V power supply or from 12V lead acid battery from your car via cigarette lighter socket.