Anybody have any experience with the internal battery? I thought I had read somewhere that they should last a couple/few years. I bought my kit used with the "low battery" (I don't recall the exact wording off-hand) warning. I replaced the battery, and here it is about 13 months later, and it's warning me again. I'm also wondering what scenarios drain it faster (ie a lot of use vs a little, plugged in vs unplugged, etc). I didn't use it too much this past year, and I always unplugged when not in use.