Some years ago Jan and I bought a Circe Helios tandem fitted with the Shimano Steps motor. We haven't used it a great deal, but one thing I've always thought about is the possibility of buying a solo e-bike, and I always thought it would be sensible to buy one with an identical motor so that if I were on a ride long enough to require extra electrons (>40 miles or so), I could stick a second battery in the luggage. However, having a look around different bikes currently on the market, I can't find anything using what appears to be a similar battery to ours. In fact, the trend seems to be to embed the batteries within the down-tube, "for aesthetic reasons".
Does anyone know if there are any down-tube embedded batteries that can be taken off the bike to be charged? It seems to me to be a pretty bad idea if not, as a decent bike frame is very likely to outlast the battery cells, and it also means that if (for example) you are on a tour involving B & B, you need to take the entire bike to the plug socket rather than an easily-portable removable battery.
It's not surprising that the technology is rapidly developing, and those of us who were early adopters might find our kit obsolete, but built-in obsolescence like this is, to me, anathema to the philosophy of cycling.