In case anyone isn't aware of it, powerbanks use switching regulators to convert the battery voltage to 5v. I personally wouldn't use one for ultra hi-fi purposes if I had a choice. Also, the benefits of batteries are for things like avoiding ground loops and line noise problems. IME in almost all cases for audio, batteries aren't really necessary. There are other ways to avoid most problems that batteries would be intended to fix.
The quality of those switching regulators will vary wildly, depending on the chip and implementation and build quality. And those mAh ratings could be pure fiction, or not, depending on the vendor.
I'd rather use a 2S lithium pack followed by a linear regulator, or possibly a higher voltage battery with a switching regulator set to output 8V, then a linear regulator.
Or if I was a true believer in the magic of batteries, I might go with 4 NiMH or NiCd cells in series for a nominal 4.8V.
I'd rather use a 2S lithium pack followed by a linear regulator, or possibly a higher voltage battery with a switching regulator set to output 8V, then a linear regulator.
Or if I was a true believer in the magic of batteries, I might go with 4 NiMH or NiCd cells in series for a nominal 4.8V.