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A universal serial bus (USB) battery charger can take many forms, whether it’s a device that uses a computer’s USB port to recharge AA and AAA batteries, a device that allows you to plug small electronics such as MP3 players into your computer’s USB port for charging, or a device that connects to small electronics via a USB port but actually uses AA or AAA battery power to charge those devices. Some USB battery chargers are designed to use a computer — either laptop or desktop — as a power source while others such devices plug into an electrical outlet in a wall. A hybrid USB battery charger can support both USB and traditional wall outlet charging, so you can pick the best method for a particular situation. The best USB battery charger for you will depend on what you plan to charge and how much portability you require.
If you expect to be away from power outlets, you may want to consider a USB battery charger that does not require a power outlet. A common example is a charger that uses AA or AAA batteries to charge an MP3 player, cellular phone or wireless headset. Although they are relatively new, USB battery chargers that are powered by solar power also exist. This can be a more efficient choice because you don't have to worry about draining AA or AAA batteries in the process of charging an electronic device, only to then need to recharge the batteries. You should, however, make sure the charger can complete the task at hand in a reasonable amount of time.
If you need to charge USB devices but have access to regular power outlets, a wall charger or a hybrid charger may be the best choice for you. Some wall chargers are versatile in that they include additional connectors for devices that use smaller USB ports for charging. You may also find a wall charger that can charge several USB devices at once. If you prefer the portability of a battery-powered USB charger, you should consider purchasing a wall charger that also has a battery compartment. This ensures you'll be able to keep your devices powered in a variety of situations.
When selecting a USB battery charger for the main purpose of charging rechargeable batteries through your computer's USB port, you should consider the battery sizes it supports and the time it takes to charge the batteries. Some USB ports do not have as much power as others, including USB ports on a USB hub or on a keyboard, so you may not be able to generate enough power to charge the batteries properly. The best choice is to find a charger with a reasonable recharge time and to make note of any USB port requirements listed on the charger.