When you started talking about modifying stuff I immediately thought about a warranty violation.The manufacturer has one small battery already built-in the light fixture, so we cannot put one large battery instead of two small ones.
I have a problem. I was thinking to put one fuse (F3) inside the light fixture and one fuse (F4) inside the additional battery enclosure. But I talked to the manufacturer and he says that NEC fuse requirements are for grid-tie applications only. He is saying that our system is enclosed (not exposed); and putting an extra fuse (F3) inside the light fixture will void the warranty.
Are the NEC fuse requirements only for grid tie applications?