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Bismillahirrahmanirrahim.

It is very important to know (without seeing) laptop battery is full or not when charging. Often when charging, we don't realize our battery have been full. Nah, it is better if KDE can play sound notification when the battery is full. And more, user should be able to change the sound with customized sound. So, we can use our own voice "heei, your battery is full! Release the cable!" or similiar on the notification.

Thank you.

I'm not sure what exactly is the point here (actually not even whether you've been sober: "Bismillahirrahmanirrahim."), but as a warning:

On a modern mobile device with li-ion battery and battery life management, this is about the best way to KILL your battery.

Though batteries still don't like heat (including the one from your notebook) and the best practice is to charge them 40-50% and then store them at around 15°C, the best realistic option is to do what every lousy fool does and DO NOT DISCONNECT THE NOTEBOOK FROM AC UNLESS YOU HAVE TO (because you want to move around)
This will just cross the battery lifetime management and cause continuous de/recharges.

Handcrafted battery management is only a reasonable idea on older devices (- maybe ~2005, no idea)

--

Now, if you just want sth. like a status notification (you load the device and when full want to use it as actual mobile, so you're really waiting for it to be full):
Powerdevil actually /has/ a notification when the charge is complete.
Run "kcmshell4 notify", select "Power Management System" and for "Charge Complete" pick and sound, dialog or custom executable invocation.