When my batteries are going dead, the cursor gets really irratic. Usually I change the batteries long before it shuts itself off though. It's hard to say, but I would try changing the batteries.
As far as battery life, I've gotten a mixed bag. Sometimes they last a couple of months, but lately they've only been averaging a month. I've switched to rechargeable batteries because of this. I would consider it a must because you'll go through a lot of batteries if you don't. Just pick up a 4 pack of NIMH "AA"s and a good charger and then you can alternate the batteries in your mouse. I think Newegg is selling the Maha charger now (great charger).
I know that battery consumption is a PITA, but I think it's well worth not having to deal with the cord, especially with the way I have mine setup. The cord was always dragging and getting caught up. That's more frustrating in a different way.
Sal