NiCD batteries are different from typical alkaline batteries or lead-acid batteries. One of the main differences is the cell voltage. A typical alkaline or lead-acid battery has a cell voltage of approximately 1.5 V, which steadily drops off as it is depleted. NiCD 18650 batteries are unique. They will maintain a steady voltage of 1.2v per cell up until it is almost completely depleted. This causes the NiCds to have the ability to deliver full power output until the end of its discharge cycle.
While they have a lower voltage per cell, they have a more powerful delivery throughout the entirety of the application. Some manufacturers make up the voltage difference by adding an extra cell to the battery pack. This allows for the voltage to be the same as the traditional type batteries, while still retaining the constant voltage that is unique to NiCds.
Another reason for the NiCd rechargeable batteries to deliver high power output is that they have very low internal resistance. Because their internal resistance is low, they are capable of discharging a lot of power quickly, as well as accepting a lot of power quickly. Having such a low internal resistance keeps the internal temperature low as well, allowing for quick charge and discharge times. This feature combined with the constant voltage of the cells allows them to put out a high amount of amperage at a consistently higher voltage than comparable alkaline batteries.
One of the most practical applications for NiCd batteries is in cordless power tools. Power tools demand a high amount of power delivery throughout the entire time of use, and do not function as well with dropping voltages as a typical battery would deliver. With NiMh battery technology, power tools are able to operate at full capacity for the entire time of use, not only the first few minutes of operation. With a Lithium-ion, alkaline, or even a lead-acid battery, the power tool will perform extremely well from the start with a steady decline in power until the power tool barely works at all.