Made a huge mistake with battery - please help

I was just on the phone with my mechanic about another subject, and asked him about this. He couldn't be specific with locations, but he said Toyota uses fusible links to protect against such things. He said to first check the fuse box (should be the one under the hood, not in the passenger compartment). You're looking for something much larger than the plastic rectangular fuses. And, there may also be another type - a short piece of wire designed to melt. Go to this web page, where for just a little money, you can buy a day's worth of access to factory service manuals online:

As JoeSpareBedroom said, the problem is most likely a fusible link. Besides links in the fuse box under the hood, there may be one attached to the positive battery cable. Replace them with the correct size and amperage and you should be good to go.

I have also seen fusible links go bad in other vehicles for precisely the same reason. The ones I have seen were older and resembled a wire about two inches long if I remember correctly.