I'm working on prototyping a power bank, to be used for charging mobile devices, smart watches, ect.. It needs to be 10'000mAH.
My initial thought, since this is just a prototype and doesn't have to be in a final manufacturable state, was to use a single lithium polymer pack, 10'000mAH and at 3.7v. I would then use a boost regulator, to boost it to 5v, and use the 5v to charge the devices.
This approach is the simplest approach, and should work in theory.
I started looking at existing models, and >90% of power banks use cylindrical lithium ion cells, used in parallel and in series. The <10% that do use lipo's use them in series, at 7.4v or even higher. I assume they are doing this, because it is more efficient to reduce the voltage, than it is to increase it.
My thought with multiple cells, is that it will make it difficult for me, not controlling my battery sources, getting cells which match enough to use together.
Is my initial approach that wrong of an idea, and if so, what are your suggestions to use multiple cells (lipo or lithium ion)?