18650 12v Battery Pack

Print this bad boy off, get a mini spot welder with some nickel strips (Alternatively you can solder wires in-between, less reliable though), 4 18650's, alternate + and - on top (Refer to pictures), weld the strips onto the batteries, wrap in heat shrink and or electrical tape and BOOM got yourself a 12v battery pack (Fully charged should read out around 14.8v on a multimeter). For the + and - leads you can either weld wires on with the nickel strips or solder the leads on directly but you'll have to GENTLY scratch up the surface of the + and - terminals and throw some flux on there and a little solder then solder the wires to the terminals.