Maglite LED Conversion and Upgrade kits: The best and cheapest dropins and replacements..
Lumencraft LED Conversion Kit Compatible/Replacement for Maglite Flashlight - 3500 Lumen for 6 D Cell - High Power Upgrade with Cree LEDs - - Amazon.com
Eblcl Maglite Led Conversion Upgrade Bulb Flashlight 3d 3c 4d 4c 5d 5c 6d 6c Cell Ce Rohs Fcc Reverse Polarity Protection - Led Bulbs & Tubes - AliExpress