Here's a post from another thread showing the 2 battery packs (old plain black and new sealed grey). The new grey pack is lithium for sure - I got one to check out earlier this year, and it's labeled as lithium. If you have the old black pack, I'd recommend putting lithiums in it for max life.
Although mine originally came with the old black pack, I don't recall what type of batteries it shipped with. Lithium is rarely the wrong choice over alkaline though.
