hi there... start from the FAQ section
and then search into battery builds:
DIY Battery Project Buildshttps://secondlifestorage.com/index.php?forums/diy-battery-project-builds.36/
Leds are current driven, not voltage driven if I remember right, I'm not so good with leds... right now I'm wondering what kind of circuit / driver I'd need between the battery and the leds to power them...
Lets say that a 18650 cell is nominal 3.7V. You can make a 14.8V battery mounting them in series of 4. So your battery could be a nice 4s25p, 4 series of 25 cells (in parallel) for a total of 100 cells. Fully charged it would reach 16.8V (4.2V x 4 in series). You also decide the lowest voltage at which you use drain your batteries, lets say 3.2V, so your minimum voltage would be 12.8V (3.2V x 4). Hope this is not too advanced for you (and sorry if I went too basic!). This could be a good book to start with: "Micah Toll - DIY Lithium Batteries".
Start your research looking into battery builds, then BMSs and then chargers. I'd start from these three points, there's a forum section for each of these.
Your BMS choice depends on the battery, that's why I'd start from learning about cells and batteries first.