I remember reading about your problems with the axle pulling foward in the dropouts, and that same thing happened with my Agutta. I fixed it with a Batavus chain pull from Holland Cycles costing a couple of quid. They’ve changed the design on the later ones which are now belt drive. But the problem I think began with the upgrade to the more powerful Impulse motor which combined with rider input, and particularity when used in very hilly terrain, meant the hub nuts could not hold the axle back, and it pulled forward on the drive side in the near horizontal drop outs.I think it was pushing £40 if I remember right. Which I swallowed until it also broke after about 2 weeks and got the feeling the bike frame and mech were great but the rest was rubbish. Including the display - back of the plastic clamp broke on that, no spares and told about £250 for a new display (when the old one still works perfectly OK. Fittings were just not fit for purpose - low quality plastic rubbish both with a design flaw where they screwed to the frame - couldn't even take the stress of the Gloucestershire potholes ! Sorry but £250 to replace a display due lack of a clamp which couldn't be fixed and no reliable chainguard (which was very unusual shape and hard to substitute) = cheap junk in my eyes. However good the system and mech were if the rest of the bike can't handle a few 25-mile trips without falling apart there's no hope for the product as a "high-end item" overall !
Re the Chinese batteries, I bought the one for my Trek from BMS Battery. Spent a few months building it a couple of years ago and it's still going strong despite having been ridden very infrequently over the last year as haven't really had the chance. Was a 36V 20Ah one - still delivers loads of power although it drops a bit faster now than when I bought it - but not much. Was under £250. I think it's the luck of the draw to some extent to be honest. The chinese hub kit isn't like riding a crank drive - but it's so much more versatile for getting around and covering distance, and I have to be honest, far more fun. For some "light" exercise, I like my new pedal bike far more than I ever liked the Kalkhoff, including the Endeavour when I tried that .
It was an example of a design working fine as a pedal cycle, and fine with the less powerful Panasonic motor, but which was not changed when other parts of the bike were upgraded and the new motors were an upgrade too far.
As regards price I asked you about your bike when you were selling it and was put off because it was a step through. But if you had put it on eBay you would have got a good price. More than double the £500 you mentioned at eighteen months old. In fact Kalkhoffs hold their price very well compared to some other makes.