Disassembly may vary depending on model. First remove the plastic mount by pressing whatever release tab necessary.
On the underside are rubberized coverings on the screw holes. Remove the covering.
Click image for larger version

Name:	_1000761.JPG
Views:	215
Size:	622.3 KB
ID:	56901Click image for larger version

Name:	_1000762.JPG
Views:	227
Size:	522.0 KB
ID:	56902

There is also a couple screws where the usb port is.
Click image for larger version

Name:	_1000765.JPG
Views:	250
Size:	379.8 KB
ID:	56900

Lift up the metal heatsink housing.
Click image for larger version

Name:	_1000766.JPG
Views:	224
Size:	647.1 KB
ID:	56903

After that, pull straight out on the clear light housing to show the 18650 cells within.
Click image for larger version

Name:	_1000767.JPG
Views:	250
Size:	508.1 KB
ID:	56904