While I don't argue that it would be nice if it recharged after the level went down while still plugged in I would wonder if you need a new battery as battery gets fully charged (you say it shows 100% charged when you first check it) and when unplugged it shows critical orange.

Have you noted how long a charge lasts when it's not plugged in? If it only lasts a couple of hours (about how long it would take from when it reaches full charge to when you wake up) I would try a new battery. If the charge lasts longer perhaps charging at a different time (such as during the day or the evening) and then unplugging it when full might be a better idea.

 

mine is always at 100% when i unplug it in the morning after waking up, i plug it in around 1100pm and wake up between 8 and 9 am, it ALWAYS reads 100% when i wake up, this makes me think that the phone firmware does do this and as suggested above you simply have a piece of bad hardware be it the phone (unlikely at this point since you have had it replaced already) or the battery (last time i had a warranty replacement it did not include the battery, i would expect that policy to be the same now) or maybe even the charger.