NiCd rechargeable batteries are widely used because they are manufactured in standard sizes compatible with regular batteries. For proper operation, they must be periodically removed from the device and recharged.
NiCd batteries should be charged for a defined period of time with a specific current, typically about 1/10 of the battery capacity.
For example, a 900 mAh NiCd battery is charged for approximately 14 hours with a current of 90 mA.
The circuit includes an LED indicator that lights up only when a battery is connected.
The required input voltage depends on the number of batteries connected in series:
- 2 batteries - minimum input voltage 5 V,
- 4 batteries - minimum input voltage 7.5 V,
- 6 batteries - minimum input voltage 10 V.
The input voltage must be rectified and filtered (an external adapter can be used).
Using the supplied components, a charger for two 900 mAh NiCd batteries can be built. In this case, the input voltage should be between 6 and 7 V.

Technical Specifications:
Type: NiCd battery charger.
Battery type: NiCd.
Charging method: constant current (~ C/10).
Indicator: LED (battery presence).
Number of batteries: 2 / 4 / 6 (series).
Input voltage:
- 2 batteries: ≥ 5 V,
- 4 batteries: ≥ 7.5 V,
- 6 batteries: ≥ 10 V.
Example configuration: 2 x 900 mAh (6-7 V input).
PCB dimensions: 32 x 23 mm.

This product is a DIY assembly kit.