If you are a battery nerd like me, you’d be interested to know that the batteries in the Prius are nimh- a safe technology that’s been proven for years and years. The capacity isn’t much compared to electric vehicles, but just enough to serve its purpose and keep the low Prius price tag. One of the only changes in the plug in Prius is to the battery. The new plugin Prius battery will be much larger to compete with the volt range and capacity. Exactly how big Toyota has not released. That will probably come out as the release nears which is still a ways away and there is time for the technology to improve drastically.
The new batteries will be lithium ion to take up the same space although they will weigh about 300 lbs than the nimh’s.