1x MacBook battery cells, it's also possible to use another type of battery.
1x DC-DC converter USB module (with charging) - from eBay ~5-7$.
Electrical wires for making connections
- Solder wire (Tin)
- Soldering Iron
- Wire stripper
Step 1: Step 1
Check the Lithium cells. It's preferable to choose only the "live" cells that have at least 3+ volts stored. Avoid using cells that are over discharged or that have 0 volts as they may burst when are being recharged.
Step 2: Step 2: Solder the Cells
Solder all tested cells in parallel. Take care not to overheat the batteries as they are sensible to heat excess.
Step 3: Step 3 - DC-DC Module PCB Install
Connect the battery terminals to the DC-DC converter module, following it's provided indications on activating it. After it starts connect USB power to charge the cells.
Step 4: Step 4: Full Video Guide
All the procedure in a video.