Using the data collected by OH8STN on the Yaesu FT-891 radio power consumption, a battery pack can be picked out to provide power to the HAM radio on expeditions such as SOTA or POTA.

The pick is a battery at about 100 greenbacks, that should cover double the maximal usage of Yaesu FT-891 at , which is a complete overkill and will thus provide a very long runtime in order to be able to make a large amount of contacts. Technically speaking, emitting at is more or less good if you're transmitting from within a cave but for normal usage, it is possible to wrap around the globe with a maximal emitter output of (assuming a transmission occurring in non-environmentally crippled bands at the time of writing, namely the bands between 15 and 30) due to the wonders of the Single-Side-Band (SSB).

Of course, the battery pack can be used for any apparel that accepts as input current, such that the teardown and minor adjustments should be feasible for any other application.

All that considered, the chosen battery makes a perfect companion and branches away from the typically "blue batteries" with an additional case and convenient voltmeter. Taking a peek inside would be a good idea, to make sure that everything is in order, given that such creations commonly are delivered with just bad circuitry that needs a little patchup, as well as to potentially attach terminals for the wires required to power the equipment.

The interior of the case contains a bunch of batteries that are connected together in order to yield , with a bunch of wires connected to a battery BMS attached on top of the batteries, and with connectors leading to the outside of the box, one of the connectors providing power, the other meant to be used with a charger.

As a bonus, the battery pack is also delivered with a charger, boasting which seems dubious given its size and build.

One minor adjustment that is made is to add screws for terminals, which seems to be a simple enough catch-all solution, that can be used both for HAM radio operations as well as providing bench power for other projects. The only requirement would be that the leads are crimped with o-ring car connectors that fortunately enough are cheap, in ample supply at any car shop and fairly tough.

For an elegant connection, butterfly screws are used that make it easy for an operator to detach hardware from the battery pack if need be.

Initially, the wire from the terminals was connected to the BMS directly, bypassing the button that the power pack has available, which was deemed later to be undesirable and ended up in a rework to make the battery only apply power to the terminals in case the battery pack is switched on.

With a bit of a hassle, the terminals are rewired, with the ground going to the BMS and the hot wire being attached to the power-on button such that power will be provided to the terminals only when the battery is switched on.

One of the troubles with batteries is that they tend to drain very fast as they are used and while they drain the voltage that the battery provides starts to drop. If the voltage drops too low, then the radio might turn off completely. In this case, using the Yaesu, it was noticed that the voltage drop reached down to about but that did not seem a problem and the radio did not switch off.

Now, radios are typically associated with vehicles such that most HAM radios available all accept as input voltage but their nominal voltage is defined at . This should not be a problem and a quick test with the Yaesu reveals that the radio transmits just fine while being powered by the battery at .

For the last two reasons, it would be interesting to manage to get the power pack to output constant voltage without any fluctuations and for this purpose a buck step-up step-down converter is used that is also powerful enough to provide the amperes that the radio requires.

Maybe one of the changes made here was to drop the buck step-up and step-down aluminum shell because it was deemed that the power drain would not heat up all that much. Even so, the that are consumed by the Yaesu are only consumed when the Yaesu is keyed-in at , which is mostly rare and the stand-by current drain is negligible by comparison. For good measure a metal slice is cut up and the buck converter is then glued onto the slice with some heat-sink grease and glue.

Interestingly, it all fits back together and some of the existing foam padding from the battery case can be removed in order to slide in the buck and metal slice.