I'm not sure "burn" is quite the right word. They're stainless. The rest of the bolt, except the head, is still pristine. So...it's oxidation from the high-heat. Like the blue ring you get around a weld. Even stainless does this, apparently.
The temperatures are a bit different for stainless, but this is close enough. My bolt head is mostly brown, with a spot of purple on it. It got pretty toasty. Hopefully localized and brief enough not to have spread and caused any damage. (I haven't noticed anything amiss with the cell).
I'll keep a close eye on it.
Meanwhile, I've been working on the second half of the battery. I have the cells strapped with end plates, decided where they're going (for now, at least), and will be working on a tray for them next.
