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.