You do want it to tell you when it is done charging when you have a wireless back. When you charge by the normal charger, the phone can switch to maintenance charging when the battery is charged. It also does this when charging with the wireless back, but because the charger cannot detect when charging is done, it continues to energize the coil in the back that rests against the battery, thus continuing to heat it even after charging is done. Samsung says to remove it from the wireless charger when it is charged. One guy on these forums woke to find the sides and back of his phone noticeably bulged out and the phone not working. The battery had "herniated". Miraculously and luckily, he replaced the battery and it returned to normal shape and operation - but he was very lucky.
If you leave yours on the wireless charger while you sleep, make sure it is within reach so when it says it is done you can pull it off the charger. It would take months of all-night charging to wreck the battery, so a few all-niters should not hurt it. Now it is weird that you want it not to tell you, when I want mine to but it doesn't. Or at least I've never heard it. I just try to pull it off the charger when I roll over during the night, though I do miss it a couple of times per week.