The first thing that most external batteries will list is its power capacity. Typically this will be listed in mAh. The higher the mAh, the more power capacity the external battery will have. By comparing the capacity of the external battery to the internal battery of a device will give a rough estimate on the total amount of running time that the external battery can provide or how many times it may fully recharge the device. The only downside here is that most devices tend to list their batteries in WHr (Watt Hours). This can make determining roughly how much running time the external battery can provide. With a bit of research it is generally possible to find the capacity listed in mAh for device batteries. For instances, the iPad Air has a 8827mAh battery while the Samsung Galaxy S4 features a 2600mAh battery.
Let’s take a closer look at some possibilities of external batteries and how much running time they might provide based on the two devices. We will use two different external batteries, one a 6000mAH battery and a 12000mAh battery. In the case of the iPad Air, the larger external battery will provide over double the running time if you have it plugged in but will only get roughly 66% more running time with the smaller 6000mAH battery. In contrast, the Galaxy S4 smartphone would get triple the running time from the 6000mAh battery and an amazing five and a half times with the gigantic 12000mAh battery.
Even though a battery might have a high capacity rating, it still may not be able to properly power your device attached to it. This is especially true for larger tablets that require a higher current level to be able to charge their internal battery. After all, when you plug a battery into the device, you are essentially charging your device as if you had it plugged into the wall. If the draw of the device is greater than the output of the battery, it will not be able to charge properly or be used while attached to the device.
The standard USB 2.0 power specification is for a 500mA power output. The newer USB 3.0 specifications allows for up to 900mA. These ratings are typically fine for a smart phone but for tablets this is generally too low for their power draw to charge them if they are in use or possible at all. In fact, most of the new iPad chargers output at roughly 2.5A. So, if you want to power the device as if it was plugged into the wall, it would need a 2.5A output over the USB output port at 5V to be roughly equivalent. It will charge the device with a lower output of say 1.5A but it would take longer and could not be operated at the same time as charging.
Number of Ports
Charging the External Battery
In addition to external device USB ports, the external battery also needs a way for it to be recharged. Generally this will be done through either a standard AC adapter with a round connector that you see with many electronic devices that plug into a wall outlet or through another USB port that is designated as an input port. Why does it matter? Well, it may make charging the external battery either more or less convenient. For instance, a USB based battery input may be able to be charged through a standard USB power adapter that came for your smart phone or tablet meaning you can carry less power adapters. Than again, if it has its own dedicated power adapter, it may be able to charge the external battery faster than if it used a devices USB power adapter.
How useful is an external battery if it does not have any way of telling you how much of a charge it has in it? Many of the low cost external batteries will not include any form of display to will let you know its current charge. This means if it has been sitting for some time, it may have no available power and no way to tell if that is the case until you plug in your device and see that it is not charging. The most common method for showing the charge is through a series of LED indicator lights. The more lights available on the display will give a more detailed reading of the power levels. In rare cases, it may have a numeric display that displays the percentage.
Size and WeightOf course, the usefulness of an external battery is only as good as one is willing to carry it. If the battery ends up being larger and heavier than the device, it may be more of a hassle to carry than just bringing a charger and making sure you plug it in from time to time. The problem is that size and weight are also directly related to the capacity of the device. For instance, a 12000mAh could be over twice the size of the smartphone and weight nearly a pound which isn’t very convenient. In contrast, a 6000mAh battery could be nearly as thin and the size of a smartphone making it extremely portable but lacking the power to deal with a high power device like a tablet.
Weight and size of external batteries can also be impacted by the material used in the batteries. Lithium polymers generally offer much lower weight and size than those designed around Ni-Mh batteries. Of course the type of material used for the battery can also impact the cost of them in addition to the size.
External batteries are a great option for any individual that frequently travels to areas where they don’t have access to power for charging up their smartphones or tablets. They also make great options for extending the running time of your device in the event of a power outage. Hopefully these tips can help best match up the type of external battery to your device for the proper power and portability to make the external battery as useful as possible.