Sunday, February 25, 2018

Shrink wrapping my homebrew KX2 battery packs

Back when I built my battery packs for internal use in the KX2, I finished them by wrapping them in several layers of electrical tape.

That worked fine - for a while.

After a few months the tape started loosening to the point where, if I'd let it continue, it would no longer adequately insulate the connections at the ends of each cell. Furthermore, the adhesive was slowly migrating to the outside of the pack resulting in a tacky feel to the whole pack.

Rather than re-wrap with new tape, I did what I should have done in the first place.

85mm shrink-wrap sleeve, before & after battery packs

Various sizes of shrink wrap are available from Amazon, including 6ft lengths of sleeve sized for a 3-pack of 18650 cells of the type used in the KX2. If you order from elsewhere, be sure to get the sleeve that is 85mm wide - not the 70mm size.

Here is a link to what I use.

To wrap your battery pack, cut a 2.75" piece of shrink-wrap from the sleeve and insert the battery pack into it, taking care to route the wire and plug in such a way that it will reach the jack in the KX2 once everything is shrinked down nice and tight.

For applying heat, I use a cheap but quite effective heat gun made for just this purpose. Although not really hot by heat gun standards, it is capable of easily overheating the shrink wrap and causing it to split. Heat the wrap only as much as necessary and resist the urge to seal it "really good" like I did on my first two attempts!

Fortunately, a 6-ft length provides enough of this stuff (at a low enough price) to satisfy anyone's learning curve.

The end result is a tight and well-insulated pack of cells, none of which have any movement at all relative to the other cells in the pack.

Info/sources on making your own KX2 battery pack.


  1. I have found the protective sleeve for fluorscent lamps works well for two lithium batteries in parallel and costs maybe a $1 at an electrical outlet

  2. You had a great signal today for QRP today besides great cw call! How do you like your FA-VA4? 73’s - wb9own

    1. Thanks for the contact. I ended up not using the FA-VA4 today...the reason I brought it was to adjust the spacing of the windings on the little circuit board connected to the antenna but decided to wait until I had a more suitable jumper going from it to the antenna. The instructions have you make those adjustments to minimize SWR on 30 and 40 meters, then secure the toroids to the board with zip ties. I'll do all that later (maybe tomorrow if the rain holds off) from the backyard.

      Thanks again for the contact and 73,