I have an old 2D blue maglite that I want to bring up to speed with an led drop-in. I would prefer something with a decent runtime, but with solid output that will maintain the focus ability of the light. I have read through several threads about mag drop-ins and most of the new ones seem to be super high output with very low runtimes. I need something with a good balance that will run on standard D cell alkalines. Thanks for your help.