A power bank (external battery) is a portable device that can supply power from its built-in batteries through a USB port. They consists of rechargeable Lithium-ion or Lithium-Polymer batteries installed in a protective casing, guided by a printed circuit board (PCB) which provides various protective and safety measures.
Power banks offer convenience in charging our gadgets. Heavy gadget users often find themselves running dry on battery while out of range from a stop contact and power banks are used to alleviate such inconvenience.
Power banks are available in different sizes, shapes and types and depending on the type, can be used to charge more than handheld gadgets. This particular type of power bank for example, are designed for stationary use where stop contact placement would be awkward.
These are the specifications that make them different:
- Capacity: measured in mAh, indicates total power capacity.
- Simultaneous charging and discharging: whether the power bank can be used while it is charging.
- Number of output USB ports: specifies the number of devices that can be charged simultaneously.
- Output current rating: specifies the maximum output current that the power bank can charge your gadget with.
- Input current rating: specifies the maximum input current that the power bank can be charged with.
- Safety Protections: Over Voltage Protection, Over Charge Protections, Over Current Protections, Over Heat Protections, Short-Circuit Protections and Over Discharge Protections are generally the most common protections that we can find.
- LED Indications: Led glows that indicate the amount of energy left in the power bank.
Capacity
One of the main attribute that you’ll look for in a power bank. The capacity of power banks is measured in mAh (Milli Ampere Hours), as is your gadget’s battery. This value theoretically indicates the power bank’s total power capacity.
It is important to note however, that there is a mismatch between the expected capacity of their purchased powerbanks and the actual number of charges that they get for their gadgets. A quick rule of thumb is to assume that the real world capacity of your power bank is 2/3 of the theoretical capacity mentioned on the package.
The reason for this mismatch is that mAh is not a good unit to measure battery capacity when the voltages of the battery and charged devices are different. If the voltages between your gadgets and your power bank are the same, there would be very little mismatch in the charging. However if your power bank’s voltage is smaller in value compared to the output voltage, the capacity of your gadget’s charged battery will be lower.
Quick example: a power bank has 10000 mAh capacity at 2 volt charging output, giving a total energy of 10000mAg x 2V = 20000 mWh. Your gadget however has a charging voltage of 5V, so the capacity of the gadget’s battery while charging at 5 volt output is 20000 mWh / 5V = 4000 mAh.
In addition to this, energy is also lost into heat during the conversion process, due to the resistance of the connecting cable.
Port and Amperage
Charging ports on power banks, like charging ports on wall-warts and computers, can provide electricity at two amperage rates: 1A and 2.1A. All USB devices can use both ports, but if a device can only handle 1A of power then it will automatically limit itself to 1A on a 2.1A port and if a 2.1A device is on a 1A port it will also charge (but at a much slower rate). The average power bank user would do with a single port or a 2.1A and 1A port. Heavy user however, would need a battery pack with two high draw 2A ports.
Read also: 5 Recommended Power Banks
Battery Types
Lithium-Ion and Lithium-Polymer batteries are the most common rechargeable cell types found in Power Banks.
Lithium-ion battery gives high energy density, low discharge rate, no priming required before first use and overall cost is comparatively cheap. However, they suffer from aging even when not used. They also don’t like cold temperatures.
Lithium-Polymer batteries uses solid but flexible polymer electrolyte rather than liquid lithium electrolyte. This means that thin and lightweight designs can hold slightly higher specific energy hence good battery life and is comparatively much safer that Li-ion. Unfortunately, they have lower energy density and are more expensive to produce.
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