The creator wanted an adjustable supply that works without mains — for the price of one you can hand-build four. The core is an adjustable buck module with a coulomb-counter display; power comes from 12 × 18650 in 3S4P (12.6V) with a 3S 40A BMS. A plastic box is cut for the quick charge port, a square hole for the coulomb-counter display, round holes on both sides, vent holes and a fan slot, a battery gauge and a master switch. The charge input feeds a CC/CV buck-boost module with charge management, output set to 12.7–12.8V; two 40℃ normally-open thermostat switches in parallel control the fan (one stuck on the boost module heatsink), with the fan and gauge negatives on the boost module input. Battery 12.6V goes through the master switch into the boost module set to 36V max, then into the digitally controlled regulator module with thyristor; output leads with clips on the output terminals, the coulomb counter’s ribbon cable into the core board. Power on — charging works, the coulomb counter lights red, a multimeter on the output clips shows the knob sets voltage precisely, up to 33V; it can charge while in use, set voltage and current precisely for load tests, and work as a universal charger for all kinds of batteries.