It may or may not really be fixed. But the challenge is in defining the term "fixed." jet fuel is an incredibly dangerous material. It hasn't been fixed, but the vehicle has been designed to accommodate and contain that danger as much as possible.
Time will tell if the steps Boeing took will prevent battery fires all together, but my guess is that they have just reduced the probability of a battery fire and designed in containment measures in the event of a fire.
That may seem like poor quality hack and patch engineering. But, if it is, then you would have to say that any device that depends on a volatile fuel or high voltage electricity is just hack & patch engineering because the danger hasn't been remove from any of that. It's just been mitigated and contained.
The only real question is why all this was allowed to happen when they had problems during the initial testing of the Li-ion sub-system? All this could have been avoided if they had fixed the problems then.
Bill, I think it has been pretty well determined that the problem is an internal battery problem, not one of charging circuits or of load gone amuk. The fix aims to eliminate the risk of cell problems creating a hazard, and it also reduces the amount of electrical stress the cells are subjected to overall (e.g. allowing less discharge than before, and also less charge than before).
I can't imagine the hectic work environment those 200 engineers have been subjected to, in these months, to come up with a viable solution. And I can only guess at how many "I told you so"s there must have been, among many of these engineers, concerning the decision to go with Li-Ion to begin with? That's just a wild guess, I admit. I sure don't envy them.