Where is the corrosion,on the terminals? If thats the case all you need to do is mix a tablespoon of baking soda in a cup of warm water mix well and pour it on the white stuff.It will fizz for a while once it stops clean it with fresh water and let it dry. Do this till the terminal is clean and then you can go to an auto parts store and buy battery terminal protectant spray it on the terminal let it dry and you are off to races. It is not uncommon at all for corossion to build on the terminals and if your mechanic does the regular servicing on your Volvo I would find a new one. P.S. there is no such thing as a leak proof battery. They all have vents to release hydrogen which is a normal by-product of the batterys function.P.P.S. DO NOT SMOKE AROUND THE BATTERY IF YOU DECIDE TO CLEAN THE TERMINALS OR INDUCE ANY KIND OF SPARK. Remember films of the Hindenberg and you will know why.