Powerbank input/output voltages

RejZoR · October 2, 2018

I got myself my first larger powerbank (till now I only had tiny 2200mAh) and while I was in the process of finding one, I realized the input and output power has quite a bit of difference. I have a 10.000mAh power bank, but if you have a phone with 3000mAh battery, you won't get 3 full charges from it. Intenso, the manufacturer actually states 30% loss due to conversion and heat. So, In an essence, 2 full charges and a bit left in the end.

Looking at the specs, it's a 10.000 mAh 3.7V Li-ion battery inside. For input, I don't really care since it comes from a wall. But on the output, you actually need a circuitry that ramps up the output voltage from battery's 3.7V to USB's 5V. And that's where the major losses happen.

So, what are technical limitations of using 5V Li-ion cells instead of 3.7V and drive the charging at same voltage without upconversion? The fact no one makes 5V Li-ion cells or something else? With 5V cells you'd only need power filtering stage and that's it. No upvolting circuitry to meet USB voltages and loses so small you could probably convert power almost 1:1 from powerbank to a phone.

Mira Yurizaki · October 2, 2018

The problem with batteries is that you can't just create any arbitrary voltage and call a day. The open circuit voltage of a battery depends on its chemical composition. Lithium anode based batteries appear to be stuck at no more than 4V.

We could find a chemical composition that allows for 5V, but unless it has the energy density of lithium, it likely won't have the overall power delivery to make it worthwhile to avoid efficiency losses.