Thanks Jinjin.Sold mine on eBay last month but just you are right, mm want Watch strap and puck. Also I think I saw something about >=80% battery health (could have been other resellers than mm though!)
Mine is a recent AppleCare replacement from Apple, so has 100% battery health still.
Think I will just source a cheap official strap from eBay and send it all together. I don't want them to quibble anything and just pay up the £198, rather than send it back to me and I lose the promotional offer I have etc.