My 401 USB charger came in today - sealed connector, looks like it should work nicely. Height of the threaded portion is the same as the ring of a 'high brass' 510 atomizer (3/8" high by 1/4" diameter). It has a very small, round 'button' for the wire connections (1/16" high by 1/4" diameter) - could possibly surface mount it with a bit of epoxy on the shoulder, or by building up an epoxy / superglue 'bed' for a buried mount.
And, it also gives me a small battery charger board that could be used for an internal charger like a JS.
And, it also gives me a small battery charger board that could be used for an internal charger like a JS.