Ultralight USB Battery Bank System for MTR3b

I’ve been searching around for a battery system for my MTR3b that is simple, lightweight, durable and most of all, reliable. The simplicity of using the radio with a 9v battery is quite nice. However, I am not a fan of non-rechargeable batteries and the small capacity is limiting on week long backpacking trips. Of course, there are larger LiPo batteries which are lightweight and have larger capacities. But, then you have to deal with all the shortcomings of LiPo chemistry, have special chargers and be extremely careful with them. Again, on long backpacking trips, carrying around another charger does not appeal to me.

I then came across a thread on here about the Adafruit 5v to 12v (and 9v variant) and that got me thinking. I usually already have a USB battery bank with me while backpacking to charge my phone, headlamp and Garmin InReach. If I could use the battery pack, that would solve the additional charger issue. It would solve the capacity issue as the MTR could run for a very long time on even a “small” usb battery bank meant for phones. It would also solve the durability issue as the cells are enclosed in a case and more protected from moisture and damage.

In that thread, it was proven that the cables are viable for use. That is assuming you have a battery bank that will actually stay on with such a tiny draw from the MTR. There is the SOTAbeams “battery keep alive load” kit but that seemed at odds with my simplicity goals.

I then came across the Nitecore NB5000 battery bank and well…I think it is just about perfect. It is water resistant, 18w input and output, USB C compatible, supports passthrough charging and best of all…weighs just 4oz. This battery bank also has a built in “trickle charge” mode which is purposefully designed for low draw devices! This should keep the battery “alive” and charging even with the small draw. The only potential issue is whether it will not adapt upward on the draw when Tx from the MTR.

Anyway, this seems to be an excellent USB battery pack option for small QRP radios like the MTR or SW-3B. It is currently in route to me and I will update the thread when I get it and can test it out with the MTR3b and the Adafruit cable.


Nitecore makes good stuff. I use their headlamp that is USB rechargeable.

Another option is a PD charger that can. provide 12VDC from a PD USB battery without any step up/down conversion. I’m using this board: https://www.amazon.com/Type-C-USB-C-charge-trigger-detector/dp/B07T2858G6

That coupled with a RAV powered USB battery bank to run everything. Doing some testing in the back country on the coast of Maine this weekend. Will be interesting to see how it pans out.

Oh that’s a cool idea too. I think this bank will do PD out as it supports 18w output. I might need to pick one of these up too. Could make it much shorter than the Adafruit cable. I would love to know how it works out.

The Nitecore NU25 headlamp is amazing!

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I really like my headlamp. Nitecore makes good gear.

Just did three activations in a row with my MTR3B using one 3S 350 mAH LiPO battery from Hobbyking. I average less than 5 mAH per QSO with this radio. The battery weighs an ounce and a half. It attaches to the radio with stick-on velcro. I made an adapter for the JST plug on the battery. The battery cost something like $5 US. I have been recharging it repeatedly since 2014, hundreds of activations. The hardest part was building the adapter.

which can be seen here plugged into the DC jack of the MTR3(just below the EFHW tuner which is built into a small case with an SWR indicator), The battery seen above the radio in this photo is a 250 mAH LiPO that weighs one ounce. I was able to put a JST jack right into a right angle plug for the DC jack of the MTR3. Hope this helps. - fred KT5X (aka WS0TA)


… this is how my “hard to build” JST adapter looks like

Didn’t say it was hard to build. Said it was the hardEST part. More fun to make it without the unnecessary intervening cable :wink: - fred


I got the Nitecore NB5000 today and I am happy to report that it works perfectly with the Adafruit cable mentioned above. It also works very will with a usb variable voltage step up device too from 9v to 12v! The device stays on even though the meter says the MTR3b is only pulling 20 mA at idle.

The weight is also spot on at 4 oz. The MTR3b will run on this 5,000 mAh pack for a very, very long time and it can also be used to charge my headlamp, phone and Garmin InReach while backpacking! Physically it takes up a smaller footprint than the MTR3b.

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Hi Spencer -
I’m glad to hear that everything lights up. I wonder - with a good antenna connected to the MTR3b, what kind of noise level does all the electronics generate? Can you test with your NB5000 system and with something like a 9V battery (which should be noise free)?
73, Etienne-K7ATN

I’ve been reading this thread with great interest.

I found this step up/step down converter on eBay. Would this be a worthy substitute for the Adafruit cable? It provides more versatility in output voltages, and the terminals allow connecting any load. Am I missing a drawback to using this device?

DC-DC Buck-Boost Converter USB Step Up Down Power Supply Module 5V to 1-24V | eBay.

73 Paula k9ir

I have essentially the same thing and when I was testing it, it frequently would error out when trying to send. It would hold steady for Rx but then when I tried to send it would increased the current draw and shut off. I am not sure if mine is just a dud, but that is my experience with a Drok Buck converter step down/up device like that.

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The one in the eBay link is rated at 3W out. With it set to 9V out then it can only supply 333mA. It may also not be able to cope with a widely varying power draw.

Maybe you are going out this slightly back to front…

You want a 5V USB power source for charging phones etc. and you need a higher supply for the radio. So why not get a USB power pack that takes 18650 LiPo cells. You can put the 18650s in the pack to charge them like any other USB pack. You can use the pack to charge phones etc. Then you remove the cells and place them in an 18650 holder where you wire them in series to provide the higher voltage.

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Tnx for the feedback, Spencer. I shall save my $$ and not get this item, given your field experience ;-).

73 Paula k9ir

Hi all
You can try this one (multi voltage between 5 to 20volts on DC out)

you can find also a 50000Ma but a bit expensive !
Like F4VPX I use this one with an FT-817nd with no problem.
73 Éric

Gotta go with Fred on this one… tiny 3S LiPo packs are the way to go. They are cheap and very small/light. No voltage regulation stuff inside to create RF noise and/or fail. The chargers are also very cheap and readily available. I have an 800mah pack that has been on week long backpacking trips and provided all the power my MTR3B required.

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How much does that 3s 800 mah battery weigh WU7H?



The thing I have a hard time ignoring is that the Nitecore bank has 6 times the capacity for just 1.7oz more than that battery pack. And it can be used to charge all my other electronics on a backpacking trip. But I would like to explore Lipo batteries more for a stripped down kit.

The Nitecore NB5000 mAh rating is for each cell, so at 3.7 V. Charging packs almost always report that number because it is the biggest.

Instead, find the Watt-hour number, then divide by the voltage you’ll be using. From the NB5000 specs:

Capacity: 5,000mAh 3.7V (18.5Wh)


As a well known fictional Scottish engineer said… Ye cannae change the laws of physics :rofl: