There is some easily available information on finding the status of a battery, or weather it\'s charging or not. (GetSystemPowerStatus API or System.Windows.Forms.SystemInformat
Actually I use such a charge limiter. There is the control software - a Python script that monitors the battery level (psutil module) and controls external hardware - i.e. a switch that can be software controlled. I have Energenie and TP-Link homeplugs plus my own hardware contraption.
As it is for home use the software it's not polished at all, but with minimal effort can be adapted to any OS or hardware.
Let know if interested. The software lives here: CCC