I don't know what the forum rules are on direct merchant links, but I've bought two Specialized battery extenders on eBay for ~$400 each delivered (US). I bought the first one to make sure it was legit. The guy has sold over 20 and as I write this has two left. The price before tax is $384
The regular price is US$450 now. There was a time this year the Range Extenders were heavily discounted in the U.S. Your man must have bought a number of those and now is making profit.
I went to Ebay & looked up the term that you used; ebike "ŕange extender", instead of "battery extender". Found what appears to be a mini-gas generator. Is that what the OP is talking about? Are there conditions under which using such an "extender" would be reasable for an ebiker? Since its advertised as an Ebike range "extender" I must assume that it would need to be carried around by an ebiker as he rides. How else would such a device be used to "extend" the "range" of an ebike? Despite its small size relative to other gas generators, the "range extender"(and its fuel) seems like quite a heavy, bulky item to lug around on an ebike. Perhaps one would be useful on wilderness bike/campimg trips? Even then, I guess I cant see the advantages. Id think a folding solar panel charger arrangement would be more compact to carry, much lighter weight, and much, much easier to find fuel for! But please do fill me in on these mini-generators if Ive got them all wrong. I like the idea. I.just dont see it as very practicle. Thanks
It is a 160 Wh 48 V Specialized external battery in the format of a water-bottle used on Specialized SL e-bikes, and connected to the e-bike by a matching cable.
I happen to own four of these.
Sorry. Was henpecking out my reply and didnt see yours till after I sent mine.