In the case that your smartphone ran out of battery and you do not have any alternative power source to charge up the battery, the three battery wiring (DIY) is a great approach to survive until power restores. This DIY Charger need only a couple of wires, a USB connector and three battery to provide balanced voltage delivery.
As shown in the above diagram, you can simply connect three 1.5V AA battery in series (one behind another) to make the temporary power source. You can get this AA Battery from the grocery store or from Amazon. If not, this will work with AAA Battery too that is available on TV remotes. Since this AAA battery has a very low capacity, it may not be capable to charge the phone for a long time.
You can remove the USB head from the Phone Charger USB cable and take out a little of the wires from the insulation. Check for the power transfer wires (Black – Negative pole, Red – Positive pole) and connect them to the battery poles accordingly. Make sure you connect the right end to the right pole of the battery to avoid malfunction and smartphone battery damage. Do not try to increase the number of batteries, which will change the charging voltage so the life of the smartphone battery.
To make your life easy, and avoid any confusion in battery settings and wire connection, we recommend you to use the battery holders. They have the slot for three batteries and output wires which you can connect externally to the charger wires. You can also buy the ones with an inbuilt USB port so that you can connect your smartphone charger directly into the box after inserting three AA batteries. Get a 3-battery cell holder from Amazon for 7 bucks.