YouTuber GreatScott! and Elektor teamed up to design a single-cell LiPo power bank with a switchable 5V 1.5 A or a 12 V 0.75 A output voltage. It is protected against overvoltage, overloads, and short circuits.

The device comes as an SMT kit, it is up to you to solder the passive components. All the difficult parts have been presoldered for you.
 
 
More information about the DIY LiPo Supercharger Kit 

Details: DIY LiPo Supercharger Kit 

Kit contains 1 mainboard pre-assembled with the 4 ICs, 15 resistors, 3 LEDs, 13 capacitors, 2 switches, 1 USB-C on a breakout board, and 2 diodes.
 

Some key specificiations: 
 
  • Battery: Single-cell lithium-ion or lithium-polymer battery
  • Input Voltage: 5 V/2 A max.
  • Output Voltage: 5 V/1.52 A; 12 V/0.76 A
  • LiPo Protection: XB8089D
  • Overcharge Detection: 4.250 V
  • Overcharge Release: 4.10 V
  • Overdischarge Detection: 2.50 V
  • Overdischarge Release: 3 V
  • Overcurrent Detection: 10.0 A
  • Thermal Shutdown: Auto-retry
  • Enable/Undervoltage Lockout: Rising: 1.2 V (typ.); Falling: 1.1 V (typ.)