Backstrap - A Heltec V3 Lora Radio with Removable 18650 Battery

Backstrap is a compact Heltec V3 case with a swappable 18650 battery and magnetic battery cover. This case makes use of the antenna and battery components that come with the Heltec, and is compatible with the optional provided headers.

This model is mildly challenging and rewarding- it requires soldering, general electrical knowledge, firmware flashing, etc. Tolerances on this print are tight with assembly gaps dialed in at 0.25mm. Know any potential limitations of your filament and printer before attempting.
Exceptionally compact at 38mm Width, 38mm Depth, 90mm Height without antennas.
The battery is a standard 18650, used in many flashlights and other off the shelf gadgets. The battery is easy to swap with a sturdy magnetic cover. This setup doesn’t interfere with the USB-C port, and USB charging also works great!
Backstrap has two options for an outer shell. One is plain, the other features a simple grip texture inspired by the geography defined lines of a topographical map. The top of the shells have a slot that measures 26x3mm at a 45 degree angle, this is perfect for a Molle strap to attach the radio to a backpack.
The OLED is protected by an inexpensive 30mm watch crystal embedded in a printed cover.

.3MF, .STEP, and Fusion file included.

PARTS:
One Heltec V3 LoRa Board:
https://amzn.to/43ucSpG
If you want a better quality antenna than the one that comes with your Heltec, this Muzi Works 915MHz LoRa antenna is fantastic:
https://amzn.to/4kBxiDi
To protect the OLED, an optional 30mm quartz watch crystal is used, though you could opt to purchase a slightly more expensive sapphire glass for more scratch resistance and strength:
https://amzn.to/4iY103u
Two M3 screws are used to secure the parts of the finished radio together- hex cap style are preferred.
https://amzn.to/4l5Wi5w
Two M3 heat set inserts are needed. Lengths between 3-8mm work well. I used 6mm like these:
https://amzn.to/4l9xMkk
One battery contact uses a 7mm disc magnet. Thickness between 1.5mm and 2mm are acceptable:
https://amzn.to/3FJ2Bfq
The other battery contacts requires one 7mm⌀*10mm compression spring.Wire thickness between 0.5-0.8mm is recommended.
https://amzn.to/3XwW51p
The back cover is attached with eight 6mm Disc magnets. Thickness between 1.5mm and 2mm are also acceptable here.
https://amzn.to/4hRcjtv
Recommended parts include CA glue/epoxy, polyimide tape to isolate soldered contacts, quality soldering flux, and a decent 18650 charger such as a NiteCore. The batteries themselves are also important- quality 18650s typically reach about 3000Mah. Many sellers online advertise 9900Mah, but this is almost impossible with modern battery chemistry in this size. When in doubt, stick to reputable brands like Samsung and Panasonic.
Finally, the filaments I used in making this project a reality:
Polymaker PolyLite ABS Grey
https://amzn.to/4j7Zkoo
And Polymaker PolyLite ABS Red
https://amzn.to/3Y5MSND

As of June 10th, 2025. Backstrap is now licensed as a Public Domain Dedication.

If you greatly enjoy this model, or plan to sell it- consider sending me a small donation that will help me make more free projects like this one.
www.paypal.me/OptimalObjects