As far as I know the % readout doesn't tell you how full the battery is in terms of amp hours. It just measures voltage. As soon as the voltage rises above 12.7 the readout says 100%, even if the battery is a long way from fully charged. As long as you confirmed that the battery is getting up to 13.6 or so volts during charging, and are seeing that the panel is putting out amperage, you don't really have a problem, just a bothersome display glitch. You might try disconnecting the controller from the battery, then reconnect it and see if it resets itself.
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