NiCd Rechargeable Battery Charging Basics

• Charge the battery when your device starts acting poorly. The battery will be at 1.1 volts.
• If you drain the battery completely, the cycle life will be shortened.
• Don't overcharge NiCds. A good smart charger will prevent overcharging.
• The Ni-Cd battery charging process is strongly endothermic, it cools during charge.
• Ni-Cd can charge very quickly, as the joule heating and endothermic charging balance each other.
• The coulometric charging efficiency of a NiCd rechargeable battery is approximately 83% for a fast (C/1 to C/.24) charge, and 63% for a C/5 charge.
• At C/1 you need 120% of the required energy. 1 Amp stored required 1.2 Amps used energy.
• A slower charge decreases the efficiency. At C/10 it is 55%, at C/20 it can get less than 50%.
• NiCd battery chargers should have a temperature cut off of 45 degrees C for a controlled fast charge, and 50 degrees C for an overnight or fast charge.
• When a charge is complete oxygen starts being generated at the nickel electrode. The oxygen diffuses through the separator and reacts with the cadmium electrode to form cadmium hydroxide. This causes a lowering of the cell voltage which can be used to detect the end of charge. This minus delta V/ delta t bump that is indicative of end-of-charge is much less pronounced in NiMH than NiCad, and it is very temperature dependent.