Powerbanks are popular today as our mobile gadgets are all getting smarter and need more power. Smartphones & tablets in many cases will not even last for a full day, so they need a back up power source. There are many different poer banks and battery chargers available to buy online, but it is important that you buy the correct charger for your smartphone. At first glance buying a power banks seems simple, if your phone has a 3000mAh battery and you see a power bank on sale with a 3000mAh capacity, you would be forgiven for thinking this charger would be able to give your phone one full charge – unfortunately, it’s not quite as simple as that!

When electrical power is transferred there is always some losses, mainly, but not exclusively, due to resistance and heat. Power Banks or chargers cannot transfer 100% of their actual capacity to any device, it’s simply not possible in the real world. So when considering a back up power source for your mobile phone, you need to factor in this loss when calculating how many times your phone could be charged. The difference between the power bank capacity and the actual power transferred to your phone is called the efficiency rating, these ratings will vary depending on the power bank cell type, quality and the environment. Ratings of between 80% and 90% are the current industry gold standards. However, you also need to consider the state of the battery you wish to charge. The lower its charge, the harder the power bank has to work. Once all these factors are taken into account, a good assumption of real life energy efficiency for power banks would be around 70%. This means that a 10000mAh power bank will fully charge a completely flat 7000mAh battery. Please find below some examples of popular smartphones along with the minimum power bank capacity required to provide one full charge from completely flat:-

The iPhone 6s has a smaller 1715mAh battery and would need a power bank with a 2450mAh capacity.

The Samsung Galaxy S6 has a 2,550mAh battery so would need a minimum 3642mAh capacity charger.

The HTC One M9 has a 2,840mAh battery so needs at least a 4057mAh power bank for one full charge.

The LG G4 smartphone has a removable 3,000 mAh battery so requires a 4285mAh capacity charger.

A Samsung Galaxy Note 5 also has a 3,000 mAh battery (non-removable) so needs a 4285mAh rated power bank.

Bear in mind the figures above are just the minimum required for one full charge. If your smartphone/battery size is not featured on the list above, then to work it out for yourself, the simple formula is battery mAh x 100/70 = mAh capacity required for one full charge.