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What is Battery and what meaning technical terms with batteries?

Battery is the primary power source for any electronics wireless gadget, be it a smartphone, laptop, smartwatch or tablet. Can you imagine the situation without these energy sources? We wouldn’t be able to build any wireless electronic device and have to rely on wired power source only.

Cell: A cell is an energy source which can deliver only DC voltage and current which are in very small quantities. For example if we take cells that we use in smartwatch or remote controls, it can give maximum of 1.5 – 3V.

Battery: The functionality of the battery is exactly same as that of a cell but a battery is a pack of cells arranged is a series/parallel fashion so that the voltage can be raised to desired levels. The best known example for a battery is a power bank which is used to charge up smart phones. If we ever see the inside of a power bank we can find set of batteries arranged serially/parallel based on the requirement. Batteries are arranged in series to increase the voltage and in parallel to increase the current.

Now Why DC is preferred over AC? In most of the portable electronics, AC can’t be stored where as DC can be stored without any difficulty. Even the losses due to AC power are more when compared to the DC power. That is the reason DC is preferred for portable electronic devices.

technical terms with batteries
We can’t just keep on using voltage and current alone to explain about a battery’s functionality, there are some unique terms that defines the characteristics of a battery like Watt-hour (mAh), C-rating, nominal voltage, charging voltage, charging current, discharging current, cut off voltage, shelf life, cycle life are the few terms used to define a batteries performance.

Power capacity:
It is the energy stored in a battery which is measured in Watt-hour
Watt-hour = V * I * hours {since voltage is kept constant, so it is measured in Ah/mAh}

We generally see the battery ratings as 2500 mAh or 4000 mAh while reading the specifications of a smart phone. What does that mean?? 

Example: 2500 mAh it means that the battery has a capability to deliver 2.5A/2500mA of current to the load for 1 hour. The time that the battery works continuously depends upon the load current that it consumes. So if the load consumes only 25 mA of current then the battery can stay alive for 100 hours. How is it?

25 mA * 100 hours {so 25 mA of current for 100 hours}
Similarly 250 mA for 10 hours So on…

Though the theoretical calculations seem ideal but the battery’s duration changes based on the temperature and the current consumption etc. 

Power capability:
It means the amount of current that the battery can deliver. It is also known as C-rating.
Theoretically, it is calculated as A-h divided by 1 hour.

Example: Let’s consider a battery which has 10000 mAh of power capacity.
After dividing 10000 mA hour/1 hour gives 10000 mA = 10 A = 10 C

So, a battery with 10000 mAh of capacity will have a C rating of 10 C which means the battery has a capability of delivering 10 A of current at a constant voltage (fixed voltage/rated voltage).
If a battery has 1C rating then the battery has a capability of delivering 1A of current.

Note: Higher the C rating, more the current that can be drawn from the battery.

Nominal voltage:
While defining power capacity we have a unit called Wh which can be elaborated as V * I * hour but where did the voltage gone? As the voltage of the battery will be constant and will not be varied, it is considered as nominal voltage (fixed voltage). So since the voltage is fixed only Ampere and hour are considered as the unit (Ah/mAh).

Charging current:
It is the maximum current that can be applied to charge the battery i.e., practically maximum of 1A/2A can be applied if a battery protecting circuit is in-built but still 500 mA is the best the range for charging the battery.

Charging voltage:
It is the maximum voltage that should be applied to the battery to efficiently charge a battery. Basically 4.2 V is the best/standard charging voltage. Though we apply 5 V to the battery it accepts only 4.2 V.

Discharging current:
It is the current that can be drawn from the battery and is delivered to the load. If the current drawn by the load is greater than the rated discharging current, the battery drains very fast which causes the battery heat up quickly which also causes the battery to explode. So it is cautious to determine the amount of current drawn by the load as well as the maximum discharging current a battery can withhold.

Shelf life:
There might be a situation where the batteries are kept idle/sealed especially in the stores/shops for a long period of time. So shelf life defines the time period a battery can be stay powered up and should be able to use it for a rated time period. Shelf life is mainly considered for non-rechargeable batteries because those are of use and throw. For rechargeable batteries even if the shelf time is less, we can still recharge it.

Cut-off voltage:
It is the voltage at which the battery can be considered as fully discharged, after which if we still try to discharge from it the battery gets damaged. So beyond the cut-off voltage the battery should be disconnected from the circuit and should be charged appropriately.

Cycle life:
Let’s consider a battery is fully charged and it is discharged to 80% of its actual capacity, then the battery is said to be completed one cycle. Likewise the number of such cycles that a battery can charge and discharge defines the cycle life. The more the cycle life the better will be the battery’s quality. But if a battery is discharged to say 40% of its actual capacity considering the battery is fully charged initially, it cannot be considered as a cycle life.

Power density:
It defines power capacity of battery for a given mass of volume.

For example 100 Wh/Kg (Alkaline battery standard power density) implies that for 1 Kg of chemical composition it provides 100 Wh of power capacity.

Now, volume of a AAA alkaline battery is 11.5 grams. So if 1Kg can give 100 Wh capacity, then how much a 11.5 gram AAA batery can give?? Let’s calculate.

Wh (for 11.5 gm) = 100*11.5/1000 = 1.15 Wh

So, we know the nominal voltage of alkaline battery is 1.5V. So it provides 1.5V * (1.15/1.5)A * 1 hour gives 0.76 Ah = 760 mAh of power capacity which is almost equal to the power capacity of a standard AAA alkaline battery.

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