The world is now becoming more and more 'mobile', which calls for use of electrical energy storage. Right form the early days of portable electronic gadgets till today, the use of battery as an electrical energy storage device has been persistent. Though a lot of research and variation has taken place from the initial stage to what it is today. With more research still going on, we can expect even more compact energy storage options and better efficient batteries that last longer and very strong.
Let's look at the development history of the energy storages for mobile electronic devices:
Wet-cell nickel-cadmium batteries were invented in 1899. Sealed NiCd cells were at one time widely used in portable power tools, photography equipment, flashlights, emergency lighting, hobby R/C, and portable electronic devices. Although the batteries could give out a lot of power instantaneously without being damaged, Ni–Cd batteries suffered from a "memory effect" if they are discharged and recharged to the same state of charge hundreds of times. The apparent symptom is that the battery "remembers" the point in its charge cycle where recharging began and during subsequent use suffers a sudden drop in voltage at that point, as if the battery had been discharged.
In 1980, the American physicist Professor John Goodenough invented a new type of lithium battery in which the lithium (Li) could migrate through the battery from one electrode to the other as a Li+ ion.Lithium is one of the lightest elements in the periodic table and it has one of the largest petrochemical potentials, therefore this combination produces some of the highest possible voltages in the most compact and lightest volumes, which makes it the most suitable type of battery for Mobile Electronic Applications like cell phones, radios, calculators etc.
Generally Lithium Batteries used in Portable Electronic Devices these days are either
- Lithium Ion
- Lithium Polymer
The following image is a single cell Li-Ion Battery.
Some important facts about a battery to note are:
Capacity: The capacity of a battery is defined in terms of Ah (Ampere hours). The Ah rating can be understood in a simple fashion with an example. Let us consider a battery with rated capacity of 4000mAh (4Ah). The amount of power stored in the battery would only last for an hour if the battery is discharged at a rate of 4 Amperes, also the same battery could also last for 10 hours if the current drawn from the battery is 400 milli-Amperes.
Depth of Discharge (DOD): This is a number given in terms of % of the total capacity of the battery. Generally for a lithium battery/cell it is stated that the DOD should be 80%
Battery Life Cycle: A battery's life is defined by the number of cycles it can run. What is a cycle? Well one full charge and one full discharge till the specified DOD constitutes one cycle.
State of Charge (SOC): SOC is defined as the status of available energy in the battery and usually expressed as percentages. Because the available energy change depends on different charging/discharging currents, temperatures and aging effects, the SOC could be defined more clearly as ASOC (Absolute State-Of-Charge) and RSOC (Relative State-Of-Charge). Typically, the range of RSOC is from 0% to 100%, a fully charged battery’s RSOC is always 100% and a fully discharged battery has 0% RSOC. The ASOC is a reference calculated by Design Capacity which is a fixed capacity from when the battery is manufactured. A fully charged new battery will have 100% ASOC, but a fully charged aging battery could be less than 100% because of different charge/discharge conditions.
About the Myth:
It has been seen that people often complain that their battery life is very poor, and a general solution given to it is for them to charge the battery to 100%, then discharge it completely and then charge it back, which would make the battery last long.
Also another general condition that people refer to is the memory effect i.e., the battery forgetting its original capacity and performing lesser than it should.
Facts to Bust the Myth:
Since the only way to monitor the amount of capacity left in a battery, is the voltage, the devices always keep a track of the voltage to give you the % remaining on the battery.
Since the capacity to the voltage graph is very flat (show in the graph below), the estimation based on voltages have slight errors. Also the voltages levels are greatly affected by the charge and discharge currents.
From this graph, we can find that as the DOD increases towards 100% we can see that life expectancy of the battery reduces. Also, from the graph we can deduce that keeping the DOD to somewhere around 40-50% would yield optimum battery operation and en-longed life, but this is a complete user preference with respect to the DOD.
Therefore, as you can see, the battery lasting long or not is completely depend on your usage patterns. Specifically in terms of Android Phones, there could be elements of the software that keep the processor busy, which leads to an unusual higher discharge current being drawn from the battery.
Now let's move on to the capacity. Since the battery is an electro-chemical device, it is liable to aging.
As you can see from the graph, as the no. of cycles completed by the battery increases, there is a drop in the capacity seen. As you can see the drop in the capacity is not very high.
Also the fact that Li-Ion batteries are unaffected by "memory effect" is clearly seen.
Coming to the final point, what exactly does the charging to 100% and Discharging do?
Well, like I mentioned, the battery % shown is just an estimation based on the voltage of the battery, frequent charging from random % to a not full voltage, gives rise to an error in the estimated capacity of the battery, therefore facing random % drops on reboot, quick discharges etc.
What exactly happens is that the estimating algorithm loses its reference that it is supposed to track and therefore gives misleading results, which is often mistaken as memory effect, but is just a calculation glitch.
Finally, the verdict is that, smartphones these days use Li-Ion and Li-Po Batteries which do not have memory effect and also the %'s shown by the phone are just an estimation based on the battery voltage, which could go wrong and hence a simple 100% charge to full discharge helps reorient the estimation of battery and does not really increase the battery life. The battery life is completely depend on the usage profile of the user.
Battery University, Google for Images.
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