At your asking price I suspect you will be keeping it, a brand new 400Wh Bosch battery with full warranty achieved just £360 + £30 delivery on Ebay recently. Ebay item number 112027540432. This all happened before the Brexit!
The seller confirmed to me they are an e-bike reseller and that the warranty from Bosch was intact. I topped out at £350 so someone else got it.
Not a bad thing to have in reserve though, just rotate the batterys so that you don't end up with one standing unused for months on end. I hope to pick one up at sometime so I can complete occasional 80 mile round trip journeys without having range anxiety or loosing several hours to re-charging the single battery before my return.