I had a similar predicament to OP. Here's how I resolved it;
In Japan I bought a Panasonic e-bike (BE-1ELSW013G) and was not allowed to take the battery (NKY576B02) home to Ireland.
Back in Europe, I bought a Panasonic flyer battery NKY316B02 (aka NKY314B02 NKY312B02)
The battery slot shape was...