We still don't know.

the TCH is just to new for any batteries to be replaced.

The Prius which has been around a lot long still does not have any good data since there has not been any reported battery replacements due to battery failure. Toyota states the battery [i]should[i] be good untill past 150,000 miles. Some think it should last the life of the car. Either way, I am hoping there is a Li-ion battery available to replace mine when it goes out, and even better a plug-in conversion to go with that replacement battery.