Most nice cordless drills have a tightening feature on them. You simple chuck the bit holding the chuck in one hand and forward trigger till tight, then twist a few clicks and the bit should be nice and snug.
If you are still having an issue then you may need a new chuck. Sucks, but it happens on all drills no matter how much you pay.
If you are still having an issue then you may need a new chuck. Sucks, but it happens on all drills no matter how much you pay.