Adam is correct.
There are many types of GTIs.
Some require a battery. Others do not.
The G in GTI stands for Grid.
Talk to the electric company, and everyone else involved, before making a GTI purchase.
Any GTI everyone will approve is certain have a respectable manual and tech support.
In the context of this post, 4,000W DC kind of sounds like Vo x Isc.
Or a sales pitch from the PMA seller.
G-