Haibike Yamaha battery, preferably dead

[DriveJunk]

Hi all, I have a 2016 or so Haibike Sduro RX with the 36v battery. I would like to have a range extender and I also have a bunch of 18650 cells, and I figure the cheapest way is to find a used up no good battery and put new cells in it. But a decent used one for not too much money would be good too.
Anyone have one lying around they haven't gotten around to recycling yet?

Thanks!

Anton