You will need the following parts to convert your bike to 12V:

12V 4Ah battery (e.g. YTX5L-BS)

Rubber battery strap

10A in-line fuse and a selection of crimp or solder terminals

A single-phase (2 wire) or 3-phase (3 wire) 12V regulator rated at 150W or more. A-Reg, Wassell or Podtronics all fine)

12V 4 ohm ignition coil

12V bulbs

12V horn (optional)