Hello, I wouldn't be concerned at all. I've been using the Vibe since UK release & the lithium batteries always lasted me around 6 weeks. The vibe battery level indicator will go down eventually. I usually got 1 to 2 weeks further lithium battery use after the level indicator finally dropped.
Animas switched me to the Alkaline Energiser Eco Advanced batteries & I get about the same 6 week usage as the lithium batteries but have to change as soon as the level drops.
Battery use will obviously depend on how much time you spend on your pump. I've always had an Animas insulin pump, 6 years pumping & it's do much better than mdi with a pen!! Good luck with it, it'll change things so much for the better.
Best wishes, Tux