I understand that there are several ways to check the life of the hybrid battery, but all these idiots at toyota dealers say no??
Toyota is correct. Others use individual module testing when removed to swap in better used modules in an attempt to keep an old battery going. Usually works for 6 to 18 months when they "may" repair it again. Toyota simply looks for a battery fail code. If in warranty the code is necessary to get a warranty replacement. Toyota does not do module replacements. A vendor of aftermarket modules created Dr Prius which has a paid feature to extrapolate (guess) the current battery's remaining capacity. Even if the capacity guess is close it does not really tell you how long before it codes. Loss of 5 or more mpg is a common indicator your hv battery is weak. Discharging fast at a traffic light causing the engine to restart is another common warning.
If you want the real story, you have to look at the data yourself. The best indirect way is to check the internal resistance of the cell blocks. It won't give you a perfect wear percentage, but if you compare your numbers to the factory values of a new battery, you can easily Google the reference values for your model, you'll see the gap. The other way is to measure the residual capacity. Compare the current capacity to the original nominal rating that tells you exactly how much "juice" the battery can still hold. Grab an OBDII scanner and an app like Dr. Prius it'll tell you more in five minutes than the dealer will in an hour.
