The only thing that you need here is OTG cable or OTG adapter which is not difficult to find, you can get this OTG adapter in almost all the mobile accessories shop or you can even order it online from AMAZON or EBAY for less than 1 dollar. I bought my OTG adapter for Rs30 or 0.5 dollars.
Basic use of this OTG adaptor or cable is to connect a USB pen drive, keyboard, mouse or a gamepad to a phone or tablet. So I was wondering if it could power keyboard or mouse why can’t it charge another phone or tablet, after all, the output of this OTG cable is 500milli ampere which is sufficient to charge any phone or tablet.
Another accessory that you need is the USB data cable which almost everybody has. Make sure that you are using a high quality data cable having a good protection in case of reverse current on smartphone.
Connect OTG adapter or cable to one phone from which you want to extract the charge. Connect the USB end of the data cable to the OTG adapter end and the other end of the data cable to the phone that you wish to charge.
After making the connections your device will start charging. Make sure that your device supports OTG adapter if your device does not recognize the OTG adapter then this method may not work. I have tested this method with various devices and it worked perfectly fine. The best part of this trick is both the device can be actively used when the charge is being transferred which is a great thing.
Charging a device with this method provide a constant output of 5 volts and 500 mill amperes of current which is pretty standard for most of the android devices. If you are using this method to charge a bigger device then definitely charging would be slower. The charging speed with this method provides a charging speed which we get when the device is connected to the computer since USB port of computer and OTG adapter is same i.e., USB 2.0 which means same voltage and same current ratings.
All the smartphones does not support OTG, if your device is not compatible with OTG then this feature may not work on your phone. Before using this feature, be sure to check for the OTG compatibility of your smartphone model.