The Problem With Power Banks – Energy Efficiency


I use power banks (also known as battery packs or portable chargers) to charge my phone and tablets, especially when I’m travelling. Back when I was using my iPhone 6, my battery would die very quickly before the day ended, and if I wasn’t in the office I would have to resort to using a battery pack.

While battery packs bring convenience and can charge our precious smartphones when we most need it (it’s like finding a restroom when you really need to pee), battery packs are a terrible waste of energy and more harmful to the environment than simply getting a phone with a larger battery capacity (seriously, if a 2mm thicker phone can give me hours more battery life, I would gladly accept that). Here’s why battery packs are so bad:

Battery packs result in double-charging, which wastes electricity!

No battery pack is 100% efficient at charging or discharging – that’s why you cannot fully charge one battery pack with another (otherwise it would be equivalent to a perpetual motion machine).

According to Wikipedia, lithium-ion batteries (used in all mobile batteries) are about 80-90% efficient. The best lithium ion batteries like electric cars and the Tesla Powerwall are up to 90% efficient. The small batteries in our phones and battery packs? Probably only about 80%.

To see how much energy is lost using a battery pack, consider the iPhone 7 with a 1960mAh capacity at 3.8V (7.45Wh of energy). Even if there is no energy loss in your wall plug (in reality there is energy loss, because there is an AC/DC converter that converts your wall socket power), you would still need 9.31Wh (7.45/0.8)of energy to charge it fully. If you use a battery pack instead, there is an extra 20% loss from the battery pack discharging and another extra 20% loss from when you had to charge the battery pack! So by using a battery pack, you would need a whopping 14.5Wh (7.45/0.8/0.8/0.8) of energy just to charge the 7.45Wh battery in your iPhone! That’s a nearly 50% total loss of energy!


This is different from having an extra removable battery in your phone (which old phones used to have) or your camera. If you have an extra removable battery and you charge that, when your phone battery runs out you simply swap it – there is no double-charging here compared to battery packs.

So what’s the solution?

Mobile phones with full-day battery life. Make those phones a few mm thicker, and let them last the whole day, so we don’t have to carry another heavy battery pack along just so our phones can last to the end of the day!