Hi. I have a 2008 Prius with the Touring Package. It has 31k miles on it and I've had it 4.5+ years. (I'm retired.) I never actually ever use the key. I just leave it in my pocketbook 24/7 and run the car without it in the ignition slot. Also I don't use it to lock or unlock the doors. I just push the door handle button. Question: Can anyone tell me what the average life span of the battery might be? Also, is there any kind of warning when the battery is getting low? Yes, I read the Owner's Manual about the key fob but it didn't address any of my questions. Any feedback is appreciated. Thank you.