When moves require a back charge, or a down charge, you’re able to charge both when you put the stick in a crouch block position. So if you put your stick in the down-back position, you have both charges. In the case of Balrog’s headbutt, if you move the stick from down-back to up-back and press punch, you’ll get a headbutt, but you’ll still maintain the ‘back’ charge so that you can do an ultra as soon as you land.
Using a charge character takes some getting used to, since a lot of your time is spent finding ways to stay mobile, while learning when and where to maintain charge and how to quickly use these moves and begin charging again. An example would be to put your stick in the down-back position as soon as you jump. This way by the time you land, you’re a split second away from having access to all of your charge moves, which allows you do combos that involve charge moves.