sport rims

Hey guys , im in need of advice here , the current NS40 battery in my Myvi is getting weaker ,thinking of upgrading it to a larger one which is NS60/L ,what i need to do/mod to get NS60 in there ?

The reason that i wanna upgrade the size is every year or so i require to replace the battery , everytime is the electrolyte inside dried out no matter i use the MF one or the normal one ,normal one after few weeks can see the electrolyte decreasing at a rapid rate already .

Which one is...