You did't say what ma 4.8 volt battery you are asking about.
A 500ma pack can be left on charge for several days.
A 250ma or less battery should not be left on charge more than 8 hrs. whereas a 1000ma pack should be charged 24hrs.
A common formula is to charge the pack at least 10 hrs. per the 50x500 factor. known as the 10x. (50ma charger, 500ma pack=10 hrs.)
50ma charger, 1000ma pack=20 hrs.)
It is a popular notion that a battery with more than 1200ma should not be charged with only a 50ma charger.