Question

what are the differences and similarities between dry cell, alkaline batteries, and ni-cad batteries

Answer 1

Nickel-Cadmium (Ni-Cad): Nickel-cadmium cells are the most commonly used rechargeable household batteries. They are useful for powering small appliances, such as garden tools and cellular phones. The basic galvanic cell in a Ni-Cd battery contains a cadmium anode, a nickel-hydroxide cathode, and an alkaline electrolyte. The equation below shows the chemical reaction in a Ni-Cd cell.
          Cd + 2H₂O + 2NiOOH —> 2Ni(OH)₂ + Cd(OH)₂
Batteries made from Ni-Cd cells offer high currents at relatively constant voltage and they are tolerant of physical abuse. Nickel-cadmium batteries are also tolerant of inefficient usage cycling. If a Ni-Cd battery has incurred memory loss (Sec. 3.4), a few cycles of discharge and recharge can often restore the battery to nearly "full" memory.  Unfortunately, nickel-cadmium technology is relatively expensive. Cadmium is an expensive metal and is toxic. Recent regulations limiting the disposal of waste cadmium (from cell manufacturing or from disposal of used batteries) has contributed to the higher costs of making and using these batteries. These increased costs do have one unexpected advantage, however: it is more cost effective to recycle and reuse many of the components of a Ni-Cd battery than it is to recycle components of other types of batteries. Several of the major battery manufacturers are leaders in such recycling efforts.

Dry cells:  Dry cells are cells that use a solid or powdery electrolyte. These kind of electrolytes use the ambient moisture in the air to complete the chemical process. Cells with liquid electrolyte can be classified as "dry" if the electrolyte is immobilized by some mechanism, such as by gelling it or by holding it in place with an absorbent substance such as paper.

Alkaline batteries: Alkaline batteries typically use sodium hydroxide or potassium hydroxide as the main component of the electrolyte. Alkaline batteries are often used in applications where long-lasting, high-energy output is needed, such as cellular phones, portable CD players and radios, pagers, and flash cameras.