Temperature gauge(QuickSilver) on Mercury outboard

I have a question about the temperature gauge on my boat(1996 Mercury 150 EFI). It is a stock gauge with the C and H markings. While working on my boat with me, a friend accidentally hooked my electronics to the trolling batteries while they were bridged to 24 Volts! The temp gauge got stuck past the H all the way down. I took the gauge off and hooked it to the batteries again and it went back down to the C. All other gauges work fine that i can see. I fired the motor up today and the temp gauge was slowly moving up. I don't know what it should be reading though because it has no numbers. Should i replace this gauge or just keep using it.