Most rechargeable lights these days will charge from USB, and don't care whether there's a wall socket or power bank behind it. But not all of these will run while charging. There was a discussion about this on the Electronics board. I've got a Lezyne headlight that will not (technically, they do sell their own special power bank that does not connect by USB for extending runtime); I think B&M lights will run while charging. Something to bear in mind. Outbound has their Hangover off-road light that has a short runtime on its internally battery, but is intended to be used with an external power bank. They've been talking about releasing a version with road optics for quite a while [taps foot impatiently].
There aren't many lights that let you replace the cells directly, but Fenix does have
one—uses two 18650s.