Should work but 2 possible issues, 1st is the 3xaaa carriers tend to be shorter than 18650 batteries so you would need a spacer.
2nd is what light is it? as if it is a multi emitter then you may find the aaa batteries unable to deliver enough current, actually you may find that even with a single emitter if it is a well driven XM-L.
2nd is what light is it? as if it is a multi emitter then you may find the aaa batteries unable to deliver enough current, actually you may find that even with a single emitter if it is a well driven XM-L.