I had the LS-10 and, while it's a really nicely made piece of equipment, it does have that bass rolloff issue. If your goal is to capture the really low end (say a freight train or thunder), then you may be disappointed. However, I think those mics are omnis and will be able to capture ample low frequency energy. You may find that it still sounds pretty good (it really depends on what you play it back on too).
I'd just go out and try it as-is. If you're happy with the results, there is no reason to spend more money. If you find that the low end is lacking, and you want to stick with that recorder, you could add a mic preamplifier and go line in (which obviously has no rolloff). A battery box is recommended for very loud sound sources, but most likely not necessary for anything else (depending on the powering requirements of those mics).