Turns out the directions for the buc aren’t quite as precise as they might outta be. When you have to RTFM it should tell you what you need to know to achieve a specific outcome.
In the manual: short the power out and adjust output current.
NOT in manual: turn buc off. (short) Turn buc on. (adjust).
But maybe it’s just me. So far the Pi3 is pulling 5v at .5a so that battery should last about 15 hours (being a 16ah battery and all) before the battery voltage drops too far to run anything. We’ll see.