No, that's not normal...
Your battery fluid will BOIL if it is too low in one or more cells, or if you have a full charge on it for too long. Both cases are bad for it. The hydrogen gas that is emitted is VERY DANGEROUS.
1) Make sure that ALL cells are all the way up to their full markings.
2) Make sure that the charger's amperage drops down after it runs for a while.
If the battery was "dead" for four years, then it might be toast and you're at risk trying to charge it at all.
-bb