What I'm thinking, and I could be wrong, I usually am
But this joint Venture between Sony & Hydro-Québec formed a company called Esstalion Technologies in June 2014.
The Esstalion name is made from the words
energy storage system and
lithium-ion.
Esstalion is going to make a energy storage units that contains 576 Sony Li-ion batteries.
The testing for the Prototype is going to start this summer, pretty much around the same time people started getting Sony batteries back in stock
So it would make sense if they were going to use 576 batteries in each unit that they would have to start to produce them again
Side Note,
For two years Sony wanted to sale their Lithium-Ion Battery Division to Nissan, but by Dec. 2013 changed their mind and decided not to sale it.
But maybe all of this is just a coincidence