The capacitance is the amount of electric charge that is stored in the capacitor at voltage of 1 Volt.

The capacitance is measured in units of Farad (F).

The capacitor disconnects current in direct current (DC) circuits and short circuit in alternating current (AC) circuits.

2. Another important similarity between the capacitor and battery is, both of them have a series resistance.

3. Both of them can create a potential difference across the other electrical components such as a resistor.

Different circuits will require capacitors with certain values and also to posses other attributes like current capability, value range, value accuracy, temperature stability and many other aspects.
Some capacitor types will be available in different values, some capacitors may have large value ranges, others smaller. Other capacitors may have high current capabilities, others high levels of stability, and others still are available with very low values of temperature coefficient.

Understanding the different ways in which capacitors are used, helps to enable the selection of the best sort of capacitor for the given application.

By selecting the right capacitor for a given use or application, the circuit can be made to perform to its best.

Primary batteries exist in different forms ranging from coin cells to AA batteries. They are commonly used in standalone applications where charging is impractical or impossible. A good example of which is in military grade devices and battery powered equipment. It will be impractical to use rechargeable batteries as recharging a battery will be the last thing in the mind of the soldiers. Primary batteries always have high specific energy and the systems in which they are used are always designed to consume low amount of power to enable the battery last as long as possible.

Secondary Batteries - are batteries with electrochemical cells whose chemical reactions can be reversed by applying a certain voltage to the battery in the reversed direction. Also referred to as rechargeable batteries, secondary cells unlike primary cells can be recharged after the energy on the battery has been used up.

They are typically used in high drain applications and other scenarios where it will be either too expensive or impracticable to use single charge batteries. Small capacity secondary batteries are used to power portable electronic devices like mobile phones, and other gadgets and appliances while heavy-duty batteries are used in powering diverse electric vehicles and other high drain applications like load levelling in electricity generation. They are also used as standalone power sources alongside Inverters to supply electricity. Although the initial cost of acquiring rechargeable batteries is always a whole lot higher than that of primary batteries but they are the most cost-effective over the long-term.