Almost any shop or dealer can use a scan tool and check on the status of the battery by looking at the difference in voltage and internal resistance of individual modules. It is expensive to replace the high-voltage battery and many experts recommend purchasing a new high-voltage battery from a Toyota dealer if, or when, it has been proved to need replacement. Even though the high-voltage battery is degraded, the vehicle can still function by using the gasoline engine more than usual resulting in reduced fuel economy. I own two hybrid electric vehicles myself and one is ten years old and is still in good health. Don’t worry about it and just enjoy it.
Have an automotive question? Get a straight answer by writing to Jim at firstname.lastname@example.org