Consider testing the battery voltage.. at the battery itself.. with a known good meter.
There are two possible issues... your controller is overcharging, or the display is reading high. If I understand you correctly, the display is integral to your controller, so there are m..ulitiple grounds for suspicion there.
It might be something as simple as a bad or corroded connection between your controller and your battery,.
IanP, the man from Scotland
Julie, the Lady From Little Rock
Jay Feather 19XUD, pushing a Jeep Grand Cherokee