How power banks are made
A power bank labeled 26,800 mAh delivered 15,682 mAh in one test. The missing charge is lost to voltage conversion.
- stations
- 7
- things upstream
- 97
- raw sources
- 29
- steps from the ground
- 9
The short version
Inside a power bank sit a few lithium-ion cells, sorted so they match, welded together with metal strips, and wired to a small circuit board. That board charges the cells, protects them and steps their 3.7 volts up to the 5 volts a USB port expects. A plastic or aluminum shell closes over it, and each unit is cycled on test racks before shipping.
-
Sort the cells
Incoming lithium-ion cells are measured for capacity and internal resistance and sorted into closely matched groups. A weak cell in a pack drags the whole pack down, so matching here saves trouble later.
Goes in -
Spot-weld the strips
Thin nickel strips are laid across the cell terminals and fused in place by short bursts of current. The cells end up in parallel or in series, depending on the design, as one solid block.
Goes in -
Print and place components
Solder paste is screened onto the pads of a bare circuit board through a metal stencil. Pick-and-place machines then set down the charging chip, the voltage converter, the protection parts and the indicator LEDs.
-
Reflow the solder
A reflow oven warms the loaded board slowly and then melts the solder particles in the paste. As the solder cools, every part is fixed to its pads in one pass.
-
Wire board to cells
Workers solder the cell block to the board's battery terminals and test it as a unit. Its converter steps the cells' voltage up to USB level, and its protection circuit cuts power on overcharge, deep discharge or short circuit.
3.7 V cells, 5 V output
Goes in -
Close the shell
The pack and board drop into a molded plastic or extruded aluminum case with openings for the USB ports and lights. The halves are clipped, screwed or glued shut.
-
Age on test racks
Finished units are charged and drained on racks, sometimes more than once, to settle the cells and confirm the delivered capacity. Automated testers then check output voltage and current before labeling and packing.
Worth repeating
- Converting a 3.7 volt battery to 5 volt USB output means a power bank can in theory deliver only about 74 percent of the mAh printed on its cells.
- In 2023 the average power bank passed about two thirds of its stored energy into the device it was charging.
- US rules ban power banks from checked luggage, and units up to 100 watt-hours may go in carry-on bags.
Back to the ground
Follow every input upstream and power bank starts as these 29 raw sources.
Everything it is made of See it on the map
Open the whole family tree
Keep walking
Sources
- Battery pack (Power bank)
- Battery management system
- Surface-mount technology
- 18650 battery
- BLUETTI Factory: How Reliable Power Stations Are Made
Cite this page: "How power banks are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/power-bank