eLeaf iStick TC40W 18650 battery replacement extension

If your TC40W's battery dies, you'll want to try to replace it.
After cautiously opening the iStick case, you'll see a soldered LiIon battery and think as I did "Easy job: it's a 18650!"... Well, not so easy, because the original battery is not a 18650 (18mm x 65mm), but a 20600 (20mm x 60mm). So even if the 18650 diameter would be OK, there is not enough room in the length of the case for a 18650.
So, I designed this small extension that sits between the top plate (where the atomizer is fitte