Very straightforward battery replacement. Your photos are the key.

Mi Problema

Old battery in my wife's iPhone 3GS would not hold a charge.

Mi Solucion

The take apart went very smoothly and quickly. The only minor glitch was getting the battery positioned perfectly so that the board would fit the screw holes. It only took 2 tries but I would make certain that the battery connector area was flush - the first time -next go-around. In all, very smooth

Mi Consejo

Not really; once again, your photos and explanations of potential trouble spots are spot on and extremely well done.