Awhile back it would no longer unlock/lock from 25-30 ft. away as it had. Eventually - the problem occurred standing next to the vehicle.
Wife's 4R has a key with FOB built into it. Used the following YT video to open key and replace battery.
How to Replace keyless entry key fob battery on a Toyota Corolla Avalon Venza remote key FCC GQ4-29T - YouTube
In my case the battery is a CR2016. 3V
You can test with a VOM like any battery. One side reads + and the other is blank(-). Her original battery read 2.91V
Replaced with a new CR2016 that reads 3.27V. All is good again.
The weak battery did not affect how the 4R started - just would not lock or unlock unless you tried many times to do so. The immobilizer light would always go out when the key was inserted - indicating the immobilizer was happy with the key in spite of the weak battery.
