I just ran another device until the batteries were almost drained. They are normal alkaline batteries. I wondered if I could use the book Port as a kind of volt meter in that if I put almost dead batteries in the unit and ask it for the percentage of battery strength, it might say something like 30% or something that would approximate the battery loss. To my amazement, they have continued to register 100% for about 15 minutes of reading. So here is the question,. Does the book port simply see new batteries inserted and reset it's battery percent to 100, or is it supposed to tell me what the real strength of the batteries is? Thanks for any help on this. Neal