When the brace touched the alternator terminal the heat could have weakened the alternator internal connection and now it is close to shorting out with the alternator housing. I would get a new alternator, because there will be metal debris floating around inside and at some point you will also short out a winding (on the brushes/commutator) and be stranded again. There is a huge amount of energy in the battery, it is not worth taking a chance. With a short the battery can explode with acid all over your car... A friend at work saw one that went streight through the bonnet!

Also watch the battery for a while, even get it tested by a battery shop (but only on a digital tester) to get the real CCA capacity of your battery. Compare it to the specification for your battery to determine how good the battery is (not just that it is still good enough to start the car). If the CCA has dropped significantly below spec, then the battery it on it's way out.