LED power question

[MrUndy]

Hey, quick overview of what I'm trying to do. I bought and put a new LED emitter in my battle saber, now I have a spare orange emitter (single LED) that I'm planning on putting in a separate handle, the downside of this handle is that the standard 4 AAA battery pack can't fit in the handle. So what I'm wondering is what would be my best power option that could fit in the small space. The battery pack is literally 1/16th of an inch too large to comfortably fit inside the battery compartment. Would a single Liion battery do fit powering up the single LED emitter (I saw some chap who was running an entire board+emitter on a single Liion battery), or should I just figure out how to expand the battery hole?

[Kouri]

A single lithium-ion will work great, so long as you've got a 1ohm resistor between the cell and LED.

[MrUndy]

Thanks! Really do appreciate the help. So just to clarify since this is pretty much my first time doing something like this.

[Kouri]

Resistor can go on either end, so yeah, that works fine. The 14500 Li-Ion US sells will work fine for a single LED, but, if you're willing to experiment, you'll get more run time out of an 18500 or 18650.