The answer is maybe.
Is your Lithium pack LiFeP04? Odds are the lithium pack is not 12V, it is 12.8, or maybe 11.1, depending on the chemistry of the battery. If you don't know, then there is no way you can do it.
Some LED supplies, Meanwell comes to mind, allow you to adjust the max voltage (and current) and indeed you can use them as a battery charger. Would I do that for cobalt electrode Lithium Ion? .. not a chance, they are too sensitive. I would do it in a pinch for LiFeP04