Determine the kind of mobile device you would like to charge with the power bank and the number of devices you wish to charge. (eg. iPhone 5, iPad, Samsung Galaxy S4, Samsung Note 3, etc.)
2. Battery capacity (mAh) and input requirement (A)
Check out the battery capacity (mAh) of each mobile device you wish to charge with dual usb power bank and also the voltage input requirement (1A/2A/2.1A). Calculate and add up the total power needed to charge up your devices. Determine your usage for each individual device and add it to the total power needed.
iPhone 5 – 1440mAh
iPhone 5s – 1560mAh
iPad 4 – 10,000mAh
Samsung Galaxy S3 – 2100mAh
Samsung Galaxy S4 – 2600mAh
Samsung Galaxy Note 3 – 3200mAh
For multiple charging of mobile devices, it would be recommended to choose portable charger with both ports 1A and 2/2.1A.
3. Power bank
After total-ling up the power needed to charge up your mobile devices, now look that the power bank that caters to your needs. At the back of most packaging, it states that there will be a successful transfer rate of 85%, where the other 15% would be lost to discharge and heat.