Found this the other day and thought it might provide someone with some useful information:
THE FACTS ON BATTERY PACKS
It seems like every mobile device, from phones and tablets to mp3 players, uses a rechargeable battery. Most of these devices are designed to both synchronize data and charge the battery when plugged into a computer's USB port.
This use of standard USB connections and USB power levels (5 VDC) has spawned battery packs designed to provide power through a USB connection. Rather than plugging the USB charge/sync cable into a computer, you can plug it into a battery pack and charge your device.
Like the batteries in your mobile devices, these battery packs are rated for their storage capacity, which are displayed as a number of milliamp-hours, abbreviated as "mAh". A milliamp-hour is just what it sounds like - 1 milliamp of power over 1 hour.
Most phones have batteries that range in size from about 1000mAh. The Apple iPhone 4S uses a 1430mAh battery while the Samsung Galaxy S3 uses a 2100mAh battery. Tablets and game consoles can have even larger batteries, with the new iPad topping more than 11000mAh!
Logic says that a 2100mAh battery pack should fully charge a Galaxy S3 battery, but when you try it you find that your Galaxy's battery is only charged to about 70-75%. So where did the rest of the power go? Is the battery pack really smaller than it's rated capacity?
No, our theoretical 2100mAh battery pack from the previous paragraph does indeed have a 2100mAh battery inside. The difference is due to the voltage levels involved.
As stated above, most mobile devices are charged using a 5 VDC USB power source. However, the batteries inside the battery pack (and those inside your phone) are rated at 3.7 or 3.8 VDC, which must then be boosted to obtain the required 5.0 VDC output.
The total amount of power available in the battery is fixed. If it can maintain a 3.7 volt output for a certain amount of time, it stands to reason that it would be able to sustain a 5.0 volt output over a shorter period of time.
To make the math easier, let's imagine a 10,000mAh battery pack. With an output level of 3.7 volts is has a total "available power" of 37,000 VmAh. Using a 5.0 VDC boosted output reduces the output current by a ratio of 3.7:5.0, resulting in an output of 7400mAh at the 5.0 VDC level.
This corresponds almost identically with the real-world test results using our hypothetical 2100mAh battery described above. There is also a small amount of energy loss due to heat, the energy required to operate the LED indicators, plus the energy required to operate the charging circuitry of both the battery pack and the device being charged.
So as a general rule of thumb, you can figure that the charging capacity of any given battery pack is about 70% of the battery's rated capacity.
THE FACTS ON BATTERY PACKS
It seems like every mobile device, from phones and tablets to mp3 players, uses a rechargeable battery. Most of these devices are designed to both synchronize data and charge the battery when plugged into a computer's USB port.
This use of standard USB connections and USB power levels (5 VDC) has spawned battery packs designed to provide power through a USB connection. Rather than plugging the USB charge/sync cable into a computer, you can plug it into a battery pack and charge your device.
Like the batteries in your mobile devices, these battery packs are rated for their storage capacity, which are displayed as a number of milliamp-hours, abbreviated as "mAh". A milliamp-hour is just what it sounds like - 1 milliamp of power over 1 hour.
Most phones have batteries that range in size from about 1000mAh. The Apple iPhone 4S uses a 1430mAh battery while the Samsung Galaxy S3 uses a 2100mAh battery. Tablets and game consoles can have even larger batteries, with the new iPad topping more than 11000mAh!
Logic says that a 2100mAh battery pack should fully charge a Galaxy S3 battery, but when you try it you find that your Galaxy's battery is only charged to about 70-75%. So where did the rest of the power go? Is the battery pack really smaller than it's rated capacity?
No, our theoretical 2100mAh battery pack from the previous paragraph does indeed have a 2100mAh battery inside. The difference is due to the voltage levels involved.
As stated above, most mobile devices are charged using a 5 VDC USB power source. However, the batteries inside the battery pack (and those inside your phone) are rated at 3.7 or 3.8 VDC, which must then be boosted to obtain the required 5.0 VDC output.
The total amount of power available in the battery is fixed. If it can maintain a 3.7 volt output for a certain amount of time, it stands to reason that it would be able to sustain a 5.0 volt output over a shorter period of time.
To make the math easier, let's imagine a 10,000mAh battery pack. With an output level of 3.7 volts is has a total "available power" of 37,000 VmAh. Using a 5.0 VDC boosted output reduces the output current by a ratio of 3.7:5.0, resulting in an output of 7400mAh at the 5.0 VDC level.
This corresponds almost identically with the real-world test results using our hypothetical 2100mAh battery described above. There is also a small amount of energy loss due to heat, the energy required to operate the LED indicators, plus the energy required to operate the charging circuitry of both the battery pack and the device being charged.
So as a general rule of thumb, you can figure that the charging capacity of any given battery pack is about 70% of the battery's rated capacity.
