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Lipo batteries and the KX3

For the KX3, I bought a set of NiMH cells and the nice LaCrosse charger for my first few activations and for getting used to the radio. I have a 7aH SLA but that is too far in the opposite direction (heavy, large, still only 5W from the KX3).

It seems that in order to get the voltage needed for 10+W operation, you need a LiPo variant. What are people using successfully?

It would seem the 4S1P LiPo4 packs would provide the optimal voltage without the need for diodes, while also being safer.

The 4S LiPo batteries seem a bit lighter and cheaper.

Just curious about what works and what doesn’t.

I use A123 LifeP04 26650 cells/packs 4S1P (I made my own packs)
14.4V fully charged and you can discharge them down to 10V
Richard // N2GBR

I happen to have a free supply of Dell laptop batteries (Li-Ion) which are in a good state.
At first I made my own packs 3S2P, which are fine for 10W with the KX3.
Recently I made a 4S2P pack, but at full charge they are 16V, so too much for the KX3.
I added this automatic voltage reducer by Phil AD5X : http://www.arrl.org/files/file/QST/This%20Month%20in%20QST/April2015/SALAS%20QS4.pdf
Here a picture of my pack in use for SOTA, I did 4 activations in a row at 15W (SSB and CW) before the voltage went under the 12.8 V limit for 15W.

There is a 20A car fuse inside the pack, and I have a seperate balancing input connector for charging the pack.
73 - Luc ON7DQ/KF0CR


Hello Even just be careful when you charge a 4S1P LiPo pack they can end up at 16 volts which is to high for the kx3 . I have a couple voltage dropping diodes in series in my power lead which helps lower the voltage. My main battery is a LiFe which only charges fully to 14.3 volts and the kx3 is ok with that voltage. Its been a very reliable battery still going strong for over 100 SOTA activation’s and i always take the LiPo as a back up on my hikes. My crude voltage dropping device is standard equipment in my SOTA bag all the time.
regards Ian vk5cz …

Likewise would go for a LiFe as against a LiPo, the LiFe gives about 14.2v which is safe for a KX3 without diodes or reducers.
My Zippy 4C LiFe 4200mA battery seems to run forever when QRPing in CW mode. Even at 10W get very good usable runtime.
A balanced charge seems to be best for the LiFe’s.

I have a LiPo which will give 16v which is to high for the KX3 so used a regulator until it blew up.
Purchased the LiFe and have used it since.

Cheers, Nick

I use a 4200mAh LiFiPo4 with my KX3, gives a good 13.2V and, on the rare occasions I run SSB it seems to give me the full cajones out :o)
Recommend adding a little battery monitor (the sort that costs just a few bucks and plugs in the the balanced charging lead on the LiPo/LiFePo) just to make sure an individual cell doesn’t drop in voltage too much over a longer activation.

Michael (G0POT)


For the past three years, I have been using Bioenno Power LiFePO4 batteries with my KX3. I have two 3 A-H (14 oz- BLF-1203T & 13 oz-BLF-1203W each) and one 4.5 A-H (18.3 oz-BLF-12045W) packs. Bioenno originally included a 2A charger with the battery but now sell the charger separately for $12 (I have two 2A chargers). After a short period of loading, the no load voltage stays flat at 12.9 VDC (per KX3 supply votage display) through most of the discharge cycle.

The baterries received an extensive SOTA workout in 2014 & 2015 and heavy NPOTA usage in 2016. I have been very happy with the Bioenno products in particular and would in general recommend LiFePO4 over LiPO.

73 Rich N4EX

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A fully charged 4S LiPO is 16.8V and the KX3 will refuse to operate at that voltage, so you need to use some series dropping diodes until the battery discharges a bit.

Barry N1EU

Barry… I think Evan was referring to the LIFeP04 cells… max voltage is 14.3 // 14.4V on a 4S pack…

Agreed LiPO is above 15V fully charged and that would be a problem for many radios including the KX3.


I also use Zippy LiFePo4 4200 mAh since two years ago, after my 4S1P LiPo died. Fully satisfied now.
Michael, would you please let us know more details about the battery monitor you suggested?
73, Ruda OK2QA

There is a little plug in you can buy pop it into the balance leads and you can set a min voltage on it if required to sound if battery gets too low and check ya balance of the cells etc. I got a Lifepro 4 batt serves me well many a time but do buy the more expense chargers as iou can set limits on them too such as fully charged not over spec voltage. But don’t discharge them to much or keep them in storage under full charge.

Got mine in a little tough sarnie box and introduced a fuse system into as well.


is the one I use.

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These work well for me:

I use this one…https://hobbyking.com/en_us/hobbykingtm-cellmeter-6-lipo-life-li-ion-cell-checker-alarm.html

It tells you the voltage of each cell, the overall voltage and the delta between cells. Works for batteries with different numbers of cells and can be set up for LiPo and LiFePo. Alarms if an individual cell drops too low in voltage.

Michael (G0POT)

I think everyone else has pretty much come the same consensus of using some kind of LiFePo4 battery for the KX3. I use a 4200mAh capacity LiFePo4 and love it!

I wrote a blog article about it looking at the advantages.

73 James M0JCQ

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I’d like to get a “ZIPPY Flightmax 4200mAh 4S1P 30C LiFePo4” Pack but I can’t find one forsale in the USA? Hobbyking only has them in the UK/EU/AUS… am I missing something?

They might be out of stock at some of their warehouses. I picked a couple up in January that shipped from their “International” warehouse in Hong Kong. I don’t think they can ship batteries to the US from the other warehouses (or choose not to due to difficulty getting stock INTO those warehouses). You might have to try checking back periodically to see if they have them in stock.

-Doug, ND9Q

Why wouldn’t you get the Bienno Power pack, they are readily available in the US it seems…

RJ // N2GBR…

Good find, though the Zippys from HobbyKing run about $15 less when they are actually in stock.

-Doug, ND9Q

Not sure there is a single consensus, especially for the KX3. I see people converging on three solutions.

  1. Use the current top of the line NiMH Eneloop batteries (they change the name occasionally) inside the KX3. This works for one or two activations in a day. People who want fewer cables and fewer things to leave behind choose this. They are the heaviest option in terms of specific energy at 220-430 kJ/kg.

  2. Use Lithium-ion batteries. These have the highest specific energy (Joules per kilogram), but an inconvenient voltage, either too high (four cells in series) or kind of low (three cells in series. Specific energy is 360–950 kJ/kg. Lithium-ion batteries catch fire if mistreated. People who focus on weight choose these.

  3. Use LiFePO4 batteries. These have a convenient voltage abd have a very low chance of catching fire. They are more expensive than Lithium-ion batteries and have a lower specific energy, 320–400 kJ/kg. People who don’t mind extra cables and like safety choose these.

The fourth option is a SLAB. That is for people on their first activation. After that, they’ll get a lighter battery.