Have you sat there and watched the phone when it is charging with the wall charger or have you just noticed when you come back to unplug it, the phone is at 97% or lower? There is a circuit in the battery that prevents it from being overcharged and causing damage to the battery. When the battery reaches 100%, the circuit cuts off the charge and lets the battery drain down to about 95%, then accepts the charge until the battery is back to 100%, then lets it drain again. It continues this cycle until you unplug your battery. You may just consistently have the bad timing of coming to unplug the phone when it is between 95 and 97%. If you are watching the phone during those final stages of charging and confirm it will not go past 97%, then sorry, I have no idea why that would be happening.