When shopping for batteries of various form factors, you may want to consult the “Battery Comparison Guide” available here:
You can click the @ sign in the Review column across from each battery and follow the link to a page with the test results, the picture of the battery, what types of cells are inside, what dimensions the battery is (you can use this to determine if it will fit into your flashlight), and the conclusion on the bottom of the page which will tell you if this is a good battery or not.
When shopping for battery pulls (batteries extracted from laptop battery packs), you may want to use the “BLF Community Battery Pulls Overview Thread” available here:
It will tell you what type of cells and capacities of batteries are inside a specific laptop battery pack. Clicking the Post link in the Link To Post column will take you to a post in which a BLF member shares his/her experience with that particular laptop battery pack and shows in pictures what it looks like.
I hope you will find these resources useful.