That's kind of what I'm wondering, too. maybe try starting the car a few times, being aware of whether or not you're pushing the key in as far as possible, or having it as far away from the scan ring. It's possible that the mm or two difference is causing your problem, even if it seems unlikely. But the keys definitely don't need the battery to communicate with the immobilizer, so something else is keeping them from communicating all the time, since the chips are some version or similar model to NXP's PCF7935 (at least in my key, for my '09 Aveo Sedan).