They're perfectly legal here. Up to 500-watts. Have been as far back as they've been selling cheap chinese ones, 15+ years ago. There are some other stipulations, like needing a seat and pedals, but that's the extent of it. My other one is shaped the same as a 50cc scooter(moped, as some of you call 'em), except it has pedals, so it's legally an electric bike!
Back on topic...batteries don't appear to be completely dead. Self-discharged beyond what's safe...I'm trickle charging them at something stupidly low(safe?), ~1 watt, with a "dumb" charger. Either the charger they come with doesn't know how to deal with over-discharged batteries, or else the BMS is blocking them from charging. Probably a good thing, since who knows what will happen if you put full charging current in to a "dead" battery.
The first one has come up and stayed up. I briefly tested that the charger that came with them is now willing to charge them, but only for a few seconds. I want to bring them up gently. The second one has just started it's slow recovery. Fingers crossed, they come back to life and still retain reasonable capacity. I don't think I want to have to try and replace the cells, the way they're basically "woven" together by the bus-bars!