Somehow I doubt it :headbang: (I don't think I've seen it mentioned on the Bose forum though).
Anyway a further update.
1, The excessive bass on the BT/aux channel is pretty well documented on the Bose S1 forum. I suspect it is partly a characteristic of BT devices which are expected to be listened to on earbuds, the S1 is a full range speaker with, I suspect, a hyped bass too so the combination is sometimes a little overpowering.
2, I bought an "Allpowers Portable Power Station" off Amazon which arrived today. It looks, as expected, a bit plasticky but feels fairly solid and has a useful (if it's accurate) LCD display.
Initialy, on plugging the XR into it I was dismayed to find it introducing an unacceptable amount of digital hash into the system but some judicious gain staging has rendered it all but inaudible. So after a not very exhaustive test it looks like it will power my XR12 for several hours (showing 7+ hours powering the XR12 and a TC VoiceSolo speaker) which is quite impressive. If it works as well with the S1 it'll be a useful addition to the inventory. https://www.amazon.co.uk/gp/product/B07H4FQFQW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
BTW it arrived in a very respectable 4 days, particularly as I was given to expect it on 30th Dec....