You are probably okay, but I would like to know a few things to help allievate any worries you might have.
First, the fact that the main fuse blew is a good thing. The job of the main fuse is to protect the electrical system from this type of short or overload. I am assuming they put a charger on backwards and the main fusible link blew.
Let me know the following;
Was the fuse blown by the charger being put on backwards, i.E. Reverse polarity?
Was the charger left on for a period of time and then the problem found?
Does the car seem OK now?
Has anyone put a multi meter on the battary to test it under load?
I will keep an eye on this post for your replay and get back ASAP.
Please consider a to help us answer more questions.
Saturday, November 20th, 2010 AT 5:04 PM