How to Make a DIY Power Bank Using 18650 Batteries
The full build guide for making a DIY power bank — the steps below follow the video process in the same order.
What you need before starting
- Rechargeable Cells: 18650 Lithium-Ion Battery Cells (salvaged from old laptop battery packs or new)
- Power Module: 5V Step-Up / Charging Power Bank Circuit Module (with USB-A output and Micro-USB/USB-C input)
- Testing & Assembly Tools: Multimeter, Soldering Iron, Solder Wire, Wire Stripper, and Electrical Insulation Tape
- Enclosure: Small Plastic Project Box / Case
The full build guide for making a DIY power bank — the steps below follow the video process in the same order.
Extract and test 18650 lithium-ion cells
Harvest 18650 cells from an old laptop battery pack. Set your multimeter to 20V DC, place the red probe on the raised positive (+) terminal and the black probe on the flat negative (-) terminal. Discard any dead cells showing 0V, and select working cells that register around 3.7V to 4.2V.
Connect cells in parallel
Strip copper at both ends of short connecting wires. Solder wires across the positive terminals of all working cells together and across the negative terminals together to create a parallel battery pack (combining capacity while maintaining a 3.7V nominal output). Wrap insulation tape around the terminals to prevent accidental short circuits.
Wire the battery pack to the power bank module
Solder the positive wire lead from the parallel battery pack to the B+ (Battery Positive) pad on the power bank circuit module. Solder the negative wire lead to the B- (Battery Negative) pad on the module.
Assemble the components in an enclosure
Place the connected battery pack and circuit module inside a plastic project box or custom enclosure, cutting small access slots for the USB charging and output ports.
Test charging and power delivery
Plug a 5V charger into the input port of the module to confirm the red charging LED blinks (indicating the power bank is charging). Plug a phone or USB device into the USB-A output port to confirm the LED stays solid red (indicating it is successfully charging your device).
If something does not work
Multimeter reads 0V on cell: The internal protection circuit or chemical cell has failed; do not attempt to recharge dead 0V lithium cells.
Module gets hot or smokes immediately: Check battery polarity instantly—connecting positive and negative backwards to B+ and B- will destroy the circuit board.
Power bank LED blinks red while charging a phone: The internal 18650 cells are depleted; plug the power bank into a wall charger to restore battery capacity.