For under ¥100, a power bank with 100W output (kit rated 20000mAh 100W PD); Samsung PD tops out at 66W, measured around 60W; stickers for looks; also handy for powering a soldering iron up to 400W for a few seconds. Cells are Lishen L700, 4000mAh each, four make 16000mAh (corrected in the comments: in 4S the capacity is still 4000mAh). Materials: case bundle ¥70-odd including the 100W multi-protocol fast-charge board, 21700 4S BMS and aluminium alloy shell; four 21700 cells at about ¥5 each; fish paper; nickel strip (Maikedai); translucent charge-level sticker; plastic back cover. Build: four cells in series for 16.8V, Li-ion tape for a first hold; fish paper (front and back); out comes the old regular, the AWithZ welder, power on, weld the positive first, welding is super satisfying, beep-beep like arc welding, always keep + and − straight; 4S 4.2V to 16.8V, if the principle isn’t clear DM for the wiring diagram, reversed will burn out; fish paper after welding, tin the pads on the 16.8V BMS; solder the + / − jumper, welds must be round and full so the load spreads and they don’t pull off; BMS onto the cells, wire ends run under the tape for looks and to protect the wire; trim the strip corners so it fits in the case, leave a solder point, bend it by hand onto the pad and solder with the iron so the strip sits tight in the solder; back-side + / −, a dab of solder on the strip then a dab on the wire end is easier; 99% solder wire; trim the strip edges; tin the BMS + / − pads the same way (wire end not tinned, redo it); keep + and − straight; fish paper insulation; thermistor through and held with heat-resistant tape, it senses cell temperature to stop overheating on charge and discharge; cells and BMS into the shell, the seller includes 3M adhesive to stick between the two boards, tidy the wires as it goes in or it won’t fit, back cover on with two screws, wires not tidy so it sits a little proud and the screws have to pull it down; the shell has a front and back, stick on the dark protective shell, fit the bottom shell, done; lure-fishing and drone stickers (shouldn’t count as infringement). Test on Samsung PD 66W: 19.5V 3.1A ≈ 58W, the seller didn’t oversell, no 100W phone so 66W is the most it can test; next episode a 60000mAh one to charge a dozen phones. Comments: fake Lishen rewraps are everywhere, Pinduoduo worst of all (3); been using one for two years; how do four 4000 cells in series make 16000; what’s the board’s controller, Injoinic SW6306?; a colour screen would be nice; parts list.