Elecraft KX3 LiFePo4 Mod by K4LXY

- May 26, 2023

Elecraft’ s choice to use of NiMH (nickel-metal-hydride) batteries is really the only complaint I have about the KX3. It probably made sense at the time, but even the KX2 and the ICOM 705 use LiFePo4 (lithium iron phosphate). The original NiMH batteries provide exactly 12v which limits the power output to 5 watts or less. Also, the internal charger takes 8-12 hours and isn’t all that precise. Which in practice means I typically use an external LifePo4 battery like the Bioenno 12v 3Ah battery which enables me to run at full 15 watts.

When I travel, there are times I don’t want take an external battery so I found a KX3 LiFePo4 internal battery conversion project by Howard K4LXY. The project consists of rewiring the battery holders into two parallel packs each holding 4 3.2v AA sized (14500) LiFePO4 batteries to create a 4S2P configuration (4 Serial, 2 Parallel). Rated at 3.2v and 600mAH, the new batteries generate 12.8v and 1.2Ah of power, enough to power the radio at 10watts for a full POTA activation.

I built my KX3 originally as a kit, so I found this project pretty simple to complete. Good soldering skills and ability to read schematics are a must. Also, you cannot charge the LiFePo4 batteries with the KX3’s internal NiMH charger so I bought a USB LiFePo4 charger take with me on trips. I disabled the charger in the radios settings menu, but I should add a warning to the KX3 startup screen as a reminder for future reference.

So far, I’m pleased with the result and the project works great. Too bad no one makes higher density LiFePo4 batteries in the 14500 AA form factor, but it appears the chemistry and size of the AA is the limiting factor. I supposed you could use Li-On which packs more punch (3.7v and up to 3600 mAh each) but Li-On is not as safe for portable use.

My Build Notes. This is the original wiring for the 8 1.5v 2800mAh batteries in case I ever want to “put it back”.

I didn’t have nylon screws so I simply used electrical tape protect the batteries from rubbing on the metal screws that secure the battery holder to the radio PCB. I used heat shrink to insulate the soldered wires and hide the diodes.