Okay I just put a new battery into my Ping about 5 days ago and it is already down one bar. Called and talked to Animas Tech support and got a real sweet heart. She told me they are finding out (just recently) that Everyready Energizer has two types of lithium batteries out. One is the Ultimate it will last around 4-6 weeks, the other, called the Advanced, is made for MP3's and Phones, and cameras and will only last about 2 weeks in an Insulin Pump. She suggested 1. I switch out my battery next set change (yep I will) and 2. send a note to the Energizer Bunny asking them to change the labeling on their Ultimate battery to make it more distinctly different from the Advance. Yep already done that !
So I guess if your Battery is going quickly check and see which one you have !