Question, isn’t the heat shrink too tight? I know that you need your heat shrink to be 3-5mm wider than what you intend to wrap. If the typical diameter of a 18540 is 18.5mm, how does your 18.5mm shrink wrap fit with a bit of room to spare? I was wondering if I should go a bit bigger by 3-5mm to be safe.
No, as long as it can be pulled over the battery it is fine.
I have added a table with diameter and minimum width of the heat shrink tube for the common battery sizes. If you buy from somewhere where they do not specify that it fits a specific battery, I would recommend to get at least 1 mm extra.
That was the reason I made this tutorial. It is easy and cheap to make a good repair, instead of doing a unsafe repair.
I did play a bit around with the hair dryer, coving part of the air intake with a hand, did increase the temperature and made it faster to shrink the heat shrink, but be careful with doing it, it can damage the hair dryer.
I’ve heatshrinked well over 1000 cells, I’m quite good at it now.
I couple additional tips. Heatshrink the positive end of the cell first by rotating the cell 360 degrees in your hand. Then go to the bottom of the cell.
Secondly, heatshrink along the crease from end to end. Use a low enough temperature or point the heatgun at a distance so it shrinks slowly. This prevents a wavy effect.
After this is done, give the entire cell a quick pass over by the heatgun to shrink the rest.