Did you get a LOW BATTERY warning in your 2014+ IS350's dash? If so, here's how to replace the battery. Very easy! Applies to IS200t, IS300 and IS250 keys too.
Sorry I’m 4 years late replying to this, but replacing the battery does n it need re-programming, not sure who told you that. It only needs to be reprogrammed if you buy a new key fob.