Going back a number of years, smartphones came with a USB charger. These days, some devices do not come with a charger but instead just a lead and the customer brings his or her own charger. Many devices include technologies such as Qualcomm QuickCharge, or come with USB Type C (such as the two new Nexus devices, the 5X and 6P), which allows faster recharging and this in turn means less time with your device plugged into the wall. However, when it comes to a straightforward device that does without the faster charging technologies, is there a way to accelerate how long the device takes to recharge? Yes there can be, but there are a couple of caveats to explain. The first is that charging over the MicroUSB standard works around the device drawing current from a charger rather than the current pushing charge into the device. What this means is that if you see a charger claiming it delivers 2A of current, your device may not be able to accept this much current. When you plug the charger into your smartphone, the two devices negotiate how much current the smartphone requires and it will draw this much from the device. The other fact to consider is that chargers are not 100% efficient: the label on the charger might say it can deliver 2A of current, but it might only be 90% efficient and so deliver 1.8A of current. You can also lose current through the MicroUSB lead too.
With that in mind, how do we measure the amount of current our device is receiving from a given charger? Fortunately, there's an app for that and it's called Ampere, which is available free on the Google Play Store with optional paid-for features. When you download, install and run Ampere, the application will attempt to show you what the current draw from the battery is, or how much current is being provided to the battery depending on if your device is plugged in or not. There are a number of devices in the Settings menu and you might have to reconfigure the application depending on your device and version of Android - typically, you need to enable "Enhanced Measurement." When you launch the application, it will take a moment to measure your device current flow and this may change a little as the smartphone or tablet does different duties in the background. Once this running, you can experiment. When the device is off the charger, you can look at the difference in power draw when using different radios such as WiFi or LTE, or changing the screen brightness.
However, when the device is on charge is when Ampere comes into its own as it shows you how much current is being drawn into the battery in order to recharge it. The simplest way here is to plug your device into a charger, ideally the original one as you might expect the manufacturer to bundle the optimal charger for your device. Give the device a moment to settle down and take a look at the current showing on the screen. Now try another charger - or perhaps the same charger and a different cable - and see what the results are. If you use a higher powered charger in your smartphone - such as the 2A charger in the example above - don't be necessarily surprised if the current drawn from your device is similar to a lesser powered charger. That's by design. The lower the charge being accepted by the device, the longer it will take to recharge. Also, as the battery fills so the amount of charge accepted by the battery is reduced. Chargers tend to work at their hardest until the battery charge is somewhere from 80% to 90%, when the amount of charge they provide gradually tapers off. There's no point in testing the current provided by your charger with the battery in the high-90s as in my example above.