Powerbanks are becoming popular these days as our gadgets or devices were all getting smarter & versatile tools in our daily lives specially for various types of communications such as calls,sms,emails and other task,and these smart devices (smartphones & tablets) needs more power for them to work and last for a day as they should be. Normally the devices that needs a back up power are the smartphones & tablets these days.And most of us individually owns one.But not all people knew how powerbank works literally.And some sellers just don't explain on how their Powerbank works.And many people just end up buying the wrong specifications of powerbank that suits the need of their devices (such as smartphones & tablets).That's the reason I made this and compiled some facts gathered from different manufacturers and blogs site ,and made it into one instructables that may help some DIY'ers who planned to build their own powerbank or just buy the right one.

Step 1: How It Works? What Type of Powerbank to Choose?

Power Banks are all the rage, they came in various shapes and sizes.,but what are they for? We explore their potential, and how to choose the right one.
What is a Power Bank and what can they charge?
Portable Power Banks are comprised of a special battery in a special case with a special circuit to control power flow. They allow you to store electrical energy (deposit it in the bank) and then later use it to charge up a mobile device (withdraw it from the bank). Power Banks have become increasingly popular as the battery life of our beloved phones, tablets and portable media players is outstripped by the amount of time we spend using them each day. By keeping a battery backup close by, you can top-up your device(s) while far from a wall outlet.
The Power Banks we're talking about are good for almost any USB-charged devices. Cameras, GoPros, Portable speakers, GPS systems, MP3 players, smartphones and even some tablets can be charged from a Power Bank - practically anything that charges from USB at home can be charged from a Power Bank - you just have to remember to keep your Power Bank charged, too!
Power Banks may also be known as Power Stations or Battery Banks, too.
•What types of Power Banks are there?
-Three major types of Power Bank found on the market today:
1. Universal Power Bank. They come in many sizes and configurations which can be tailored to your device requirements and to your budget.
2. Solar-Charged Power Bank. They have photovoltaic panels which can trickle-charge the internal battery when placed in sunlight. Solar charging isn't fast, so they can usually charge via cable as well.
3. The third type of Power Bank is the older-style battery phone case. While they can be handy, this type of Power Bank has very narrow device compatibility,
•How do I charge a Power Bank?
Most commonly, a Power Bank will have a dedicated input socket for receiving power. This power can come from a USB socket on your computer, but may charge faster when using a wall socket adapter. We most often see Power Banks use a Mini or Micro-USB socket for charging, and full-sized USB sockets for discharging. On very rare occasions, Power Banks can use the same socket for input and output, but this is rare and should not be assumed of any Power Bank, as trying to force power into an output can damage the battery. Always check the manual for specific instructions if you're not able to find a clearly marked input socket.
Depending on the capacity of the Power Bank and its current charge level, it can take quite a while to fill up. For example, a 1500mAh rated Power Bank should take about the same time as your typical smartphone to charge. For larger banks, this time can be doubled, tripled or quadrupled. Most Power Banks have both an LED indicator to show when they are at capacity, and a safety cut-off to prevent overcharging and overheating. Whenever possible, remove the Power Bank from charge when it is full, or at least avoid leaving it connected long-term after its full. Ambient temperature and power flow will also affect charge times, so it's best to keep it topped off regularly.
Some Power Banks don't work well with high-capacity chargers (like the ones that come with iPads). Trying to fast-charge a Power Bank from a 2A charger can result in damage to the internal circuitry.
•How long does a Power Bank last?
This is a bit of a loaded question. There are two important life expectancies to consider:
1. The number of charge/discharge cycles a Power Bank can reliably perform in its lifetime.
2. How long a Power Bank can retain its charge when not in use.
The answer to point one can differ between models of Power Bank, their internal components and the quality of their manufacturing. We try not to stock Power Banks which have fewer than 500 charge cycles in them. This would allow you to charge a device from the Power Bank every day for a 1.5 years before it started to lose its ability to hold charge long-term. Better and more expensive Power Banks can last longer, while smaller and cheaper units may fall short depending on their treatment. Power Banks are generally not used daily, so they often last much longer than 18 months in real-world usage patterns.
Point two depends on the quality of the controller circuitry and battery cells. A good Power Bank can hold charge for 3 to 6 months with minimal loss. Lower quality Power Banks may struggle to retain a useful charge more than 4 to 6 weeks. In this regard, you get what you pay for, and if you need a long-term emergency power supply consider increasing your budget to ensure you're not going to be caught short. Most Power Banks will slowly lose charge over time, to a degree influenced by the environment and their treatment. For example, leaving a Power Bank in the car where the temperature can fluctuate greatly over time can shorten its lifespan.
•Technical Term Glossary
What does mAh mean?
Batteries common to mobile devices and Power Banks are rated on their ampere-hours, measured in milliamps to create non-decimal numbers. The mAh ratings denote capacity for power flow over time.
Li-Ion & Li-Polymer
Lithium-Ion and Lithium-Polymer batteries are the most common rechargeable cell types found in Power Banks. Lithium-Ion cells are generally cheaper and limited in mAh capacity, while Lithium-Polymer cells can be larger and don't suffer from a memory effect over time.
Efficiency
When power is transferred, there is always loss due to resistance. Power Banks are not able to transfer 100% of their actual capacity to a device, so we factor in this loss when calculating how many times an average device can be charged from a fully powered Power Bank of any given size. Efficiency ratings differ between Power Banks based on their cell type, component quality and environment. Ratings between 80% and 90% are the current industry standard. Beware of suspiciously low-cost options claiming efficiency ratings of over 90%.
Device Depletion
This is the state of the battery in the device you wish to charge. The lower its power, the more a Power Bank has to work to bring it back to life. We consider charging from 20% to 90% a full charge, as the efficiency loss increases beyond these points, leading to wasted charging potential. Going from 5% to 100% can take exponentially more power.

Step 2: Choosing the Right Powerbanks:

1.How do I know which
powerbank suits my device?
Depending on individual
needs and requirements,
there are several general
criteria to consider when
selecting a powerbank:
a) Capacity
For example if your phone battery is 1500mAh and is 0% now, a powerbank with 2200mAh can charge your phone 1 time. If your phone battery is 3000mAh and is 0% now, a powerbank with 2200mAh will not be able to charge your phone to full because the phone battery capacity is higher than the powerbank. If you require a powerbank that is able to charge your phone several times, you need a powerbank with higher capacity.
b) Number of output
1 output to charge 1 device, 2 outputs to charge 2 devices.
c) Output specification
1A-1.5A output is generally for smartphones, 1.5A-2.0A output is generally for tablets.
2. How long do I need to charge the powerbank for the first time and subsequent time?/ How many times can a powerbank charge my phone?
a) Powerbank is already pre-charged and ready to use.
b) Re-charging time depends on the capacity of the powerbank, remaining power in the powerbank and the power supply.
Example:
-Powerbank: 13000mAh (0% remaining)
-Power Supply/ Input: 1000mA plug
-Calculation: 13000mAh/ 800mA = minimum 16.25 hours
(Why 800mA? An estimate of 20% power is consumed during the charging/ discharging process)
c) Similar formula applies to calculate number of times a powerbank can charge a phone.
Example:
-Powerbank: 10000mAh (full at 90%)
-Phone Battery: 1500mAh
-Calculation: (10000mAh x 90% x 80%) / 1500mAh = up to 5 times
(Why 90%? Assuming the power bank is well maintained in good working condition and can conserve up to 90% power)
(Why 80%? An estimate of 20% power is consumed during the charging/ discharging process)
* Note that the calculation is based on normal condition whereby the powerbank or device (phone/ tablet) is not in use during charging process. A running device generally consumes power therefore if your device is actively in use during the charging process, the charging performance may not meet the expectation.
* The above calculations are examples made simple for easy reference. Accuracy may vary.

•Images in order
1.Commercial PB (upgraded from 1200 to 2800 mah)
2.Commercial PB Kit(modified by adding switch and upgraded 2400 to 4000mah)
3.Commercial PB under my testing.

Step 3: Homebrewed Powerbanks

Image1-using 8 AA Nimh 2800 mah batteries
Image2-using 3*18650 2200mah Li-ion batteries

*ibles can be found on my DIYs

Step 4: Difference Between Li-ion and Li-Po

Lithium-ion batteries use a variety of cathodes and electrolytes. Common combinations use an anode of lithium (Li) ions dissolved in carbon or graphite and a cathode of lithium cobalt-oxide (LiCoO2) or lithium manganese-oxide (LiMn2O4) in an liquid electrolyte of lithium salt. Because they use a liquid electrolyte, lithium-ion batteries are limited in shape to either prismatic (rectangular) or cylindrical. The cylindrical form has a similar construction to other cylindrical rechargeable batteries,Prismatic batteries have the anode and cathode inserted into the rectangular enclosure. The image link at illustrates this construction method. Lithium-Ion-Polymer batteries are the next stage in development and replace the liquid electrolyte with a plastic (or polymer) electrolyte. This allows the batteries to be made in a variety of shapes and sizes.
The significant advantages of lithium-ion batteries are size, weight and energy density (the amount of power the battery can provide). Lithium-ion batteries are smaller, lighter and provide more energy than either nickel-cadmium or nickel-metal-hydride batteries. Additionally, lithium-ion batteries operate in a wider temperature range and can be recharged before they are fully discharged without creating a memory problem.
As with most new technology, the disadvantage is pricing. Currently, lithium-ion and lithium-ion-polymer batteries are more expensive to manufacture than standard rechargeable batteries. Part of this expense is due to the volatile nature of lithium.
Lithium-ion batteries are most commonly used in applications where one or more of the advantages (size, weight or energy) outweigh the additional cost, such as mobile telephones and mobile computing devices. Lithium-ion-polymer batteries are used when the battery needs to be a particular shape.
________________________________________
Lithium-Ion Battery Characteristics
Type Secondary
•Chemical Reaction Varies, depending on electrolyte.
Operating Temperature 4∫ F to 140∫ F ( -20∫ C to 60∫ C)
•Recommended for Cellular telephones, mobile computing devices.
•Initial Voltage 3.6 & 7.2
Capacity Varies (generally up to twice the capacity of a Ni-Cd cellular battery)
•Discharge Rate Flat
•Recharge Life 300 - 400 cycles
•Charging Temperature 32∫ F to 140∫ F (0∫ C to 60∫ C)
•Storage Life Loses less than 0.1% per month.
•Storage Temperature -4∫ F to 140∫ F ( -20∫ C to 60∫ C)
ï The chemical construction of this battery limits it to a rectangular shape.
ï Lighter than nickel-based secondary batteries with (Ni-Cd and NiMH).
________________________________________
Lithium-Ion-Polymer Battery Characteristics
Type Secondary
Chemical Reaction Varies, depending on electrolyte.
Operating Temperature Improved performance at low and high temperatures.
Recommended for Cellular telephones, mobile computing devices.
•Initial Voltage 3.6 & 7.2
•Capacity Varies depending on the battery; superior to standard lithium-ion.
•Discharge Rate Flat
•Recharge Life 300 - 400 cycles
•Charging Temperature 32∫ F to 140∫ F (0∫ C to 60∫ C)
•Storage Life Loses less than 0.1% per month.
•Storage Temperature -4∫ F to 140∫ F ( -20∫ C to 60∫ C)
ï Lighter than nickel-based secondary batteries with (Ni-Cd and NiMH).
ï Can be made in a variety of shapes.

Step 5: Facts About Lithium Ion:

Is Lithium-ion the Ideal Battery?For many years, nickel-cadmium had been the only suitable battery for portable equipment from wireless communications to mobile computing. Nickel-metal-hydride and lithium-ion emerged In the early 1990s, fighting nose-to-nose to gain customer's acceptance. Today, lithium-ion is the fastest growing and most promising battery chemistry.
The lithium-ion battery
Pioneer work with the lithium battery began in 1912 under G.N. Lewis but it was not until the early 1970s when the first non-rechargeable lithium batteries became commercially available. lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density for weight.
Attempts to develop rechargeable lithium batteries failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, lithium-ion is safe, provided certain precautions are met when charging and discharging. In 1991, the Sony Corporation commercialized the first lithium-ion battery. Other manufacturers followed suit.
The energy density of lithium-ion is typically twice that of the standard nickel-cadmium. There is potential for higher energy densities. The load characteristics are reasonably good and behave similarly to nickel-cadmium in terms of discharge. The high cell voltage of 3.6 volts allows battery pack designs with only one cell. Most of today's mobile phones run on a single cell. A nickel-based pack would require three 1.2-volt cells connected in series.
Lithium-ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery's life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications. lithium-ion cells cause little harm when disposed.
Despite its overall advantages, lithium-ion has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs are is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.
Aging is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. The battery frequently fails after two or three years. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for nickel-metal-hydride if exposed to high ambient temperatures. At the same time, lithium-ion packs are known to have served for five years in some applications.
Manufacturers are constantly improving lithium-ion. New and enhanced chemical combinations are introduced every six months or so. With such rapid progress, it is difficult to assess how well the revised battery will age.
Storage in a cool place slows the aging process of lithium-ion (and other chemistries). Manufacturers recommend storage temperatures of 15∞C (59∞F). In addition, the battery should be partially charged during storage. The manufacturer recommends a 40% charge.
The most economical lithium-ion battery in terms of cost-to-energy ratio is the cylindrical 18650 (size is 18mm x 65.2mm). This cell is used for mobile computing and other applications that do not demand ultra-thin geometry. If a slim pack is required, the prismatic lithium-ion cell is the best choice. These cells come at a higher cost in terms of stored energy.
Advantages
ï High energy density - potential for yet higher capacities.
ï Does not need prolonged priming when new. One regular charge is all that's needed.
ï Relatively low self-discharge - self-discharge is less than half that of nickel-based batteries.
ï Low Maintenance - no periodic discharge is needed; there is no memory.
ï Specialty cells can provide very high current to applications such as power tools.
Limitations
ï Requires protection circuit to maintain voltage and current within safe limits.
ï Subject to aging, even if not in use - storage in a cool place at 40% charge reduces the aging effect.
ï Transportation restrictions - shipment of larger quantities may be subject to regulatory control. This restriction does not apply to personal carry-on batteries.
ï Expensive to manufacture - about 40 percent higher in cost than nickel-cadmium.
ï Not fully mature - metals and chemicals are changing on a continuing basis.
The lithium polymer battery
The lithium-polymer differentiates itself from conventional battery systems in the type of electrolyte used. The original design, dating back to the 1970s, uses a dry solid polymer electrolyte. This electrolyte resembles a plastic-like film that does not conduct electricity but allows ions exchange (electrically charged atoms or groups of atoms). The polymer electrolyte replaces the traditional porous separator, which is soaked with electrolyte.
The dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile geometry. With a cell thickness measuring as little as one millimeter (0.039 inches), equipment designers are left to their own imagination in terms of form, shape and size.
Unfortunately, the dry lithium-polymer suffers from poor conductivity. The internal resistance is too high and cannot deliver the current bursts needed to power modern communication devices and spin up the hard drives of mobile computing equipment. Heating the cell to 60∞C (140∞F) and higher increases the conductivity, a requirement that is unsuitable for portable applications.
To compromise, some gelled electrolyte has been added. The commercial cells use a separator/ electrolyte membrane prepared from the same traditional porous polyethylene or polypropylene separator filled with a polymer, which gels upon filling with the liquid electrolyte. Thus the commercial lithium-ion polymer cells are very similar in chemistry and materials to their liquid electrolyte counter parts.
Lithium-ion-polymer has not caught on as quickly as some analysts had expected. Its superiority to other systems and low manufacturing costs has not been realized. No improvements in capacity gains are achieved - in fact, the capacity is slightly less than that of the standard lithium-ion battery. Lithium-ion-polymer finds its market niche in wafer-thin geometries, such as batteries for credit cards and other such applications.
Advantages
ï Very low profile - batteries resembling the profile of a credit card are feasible.
ï Flexible form factor - manufacturers are not bound by standard cell formats. With high volume, any reasonable size can be produced economically.
ï Lightweight - gelled electrolytes enable simplified packaging by eliminating the metal shell.
ï Improved safety - more resistant to overcharge; less chance for electrolyte leakage.
Limitations
ï Lower energy density and decreased cycle count compared to lithium-ion.
ï Expensive to manufacture.
ï No standard sizes. Most cells are produced for high volume consumer markets.
ï Higher cost-to-energy ratio than lithium-ion

Step 6: Powerbank Accesories

•image 1 - bundled with commercial Powerbanks.
•image 2- additional(option only) accesory to extend compatibility to any devices.

Step 7: Functions of Powerbanks

•image 1- PB on portable speaker great for outdoor use.
•image2- PB on LG Prada using usb cable adapters
•image 3 - PB on portable DVD R/W optical drive
•image 4 - pendrive powerbank (single AA Nimh 2800 mah )

Step 8: Common Problems/Troubleshooting

1.Powerbank unable to charge my tablet?
a) Powerbank with 2A output to charge tablets. While some tablets can accept lower input (1A or 1.5A), the charging is slower and sometimes can only be charged when the tablet is in sleep mode.
b) Some tablet is cables might not be compatible with power bank due to different cable chipset design. For Samsung Galaxy Tab in particular, we recommend using the cable and connector meant for power bank (comes with some power banks.
2.Powerbank battery drained off very fast?
a) Generally, a well maintained powerbank can retain up to 80-90% of its original capacity. Please check your device (phone/ tablet) original battery capacity and the powerbank capacity. Please also see answer 1.a. above.
b) The number of times a powerbank can charge your device very much depends on the capacity of both the powerbank and the device. Examples of calculation shown in answer 2 above.
c) Please do not attach cables to the powerbank when not in use.
3.Unable to turn on my powerbank?
a) It is possible that your powerbank is fully drained. Please charge your powerbank. The indicator will start blinking when the powerbank receives sufficient power.
b) It is possible that your powerbank went into sleep mode. The powerbank will automatically cut-off the power and go into sleep mode when it detects possibility of over-charge/ over-discharge/ short-circuit. This is sometimes due to faulty cable issue. Please activate the ìsleepingî powerbank by charging it with its wall plug (3-pin plug) and use a good condition cable.
4.What is the lifespan of the powerbank?
Generally, a properly maintained powerbank can retain up to 80-90% of its original capacity at 400-500 charge and discharge cycle (charge then discharge = 1 cycle, regardless of whether you charge/ discharge it partially or fully). Until your power bank no longer holds sufficient charge to meet your needs, you may choose to purchase a new one.

Step 9:

http://batteryuniversity.com/learn/

Step 10: Credits to the Following Sources

And there it is,Powerbank a very useful devices that really help in time of needs.,particular when you are on outdoor or during calamities when powergrid are down.,
Hoping you like it & hopefully helped those who are interested in doing or building their own powerbanks.

•some of the DIY Powerbank shown here are available on my Instructables found here.