On our equipment if we broke a terminal we would take old lead weights we would get At a tire shop and melt them in a pipe cap, we had a piece of 1/2" pipe about 3/4" long we set on top of the broken post then pour the molten lead in and let cool then use a rasp file to shape it. Hand held propane torch works great to melt the lead

 

The real question is: Why did it break in the first place?

 

Buy a new battery. I wouldn't trust a patched battery post. Asking for problems if you botch the repair.

 

X2