The "frayed and broken earthing wire" looks like it was mechanically destroyed. I.e. somebody wanted to take the battery out in a hurry and didn't have the right tools. It is not burned/welded/melted. Somebody took a pair of pliers to it. The firemen did it.
I haven't seen any good pictures or scans of the ANA battery. I thought it was burned so bad that they couldn't really make a valid conclusion. The JAL battery was "lucky", in that they stopped the fire before complete destruction and they got a good look at the failure mode.
150 battery replacements does seem high at first, but 787's have flown thousandsof flights. Most of the CB's are "virtual" on the cockpit displays. It would not surprise me that unfamiliar ground crew would leave things powered by accident or lack of education. Especially during the day. At night you see the lights on. During the day, maybe not.