I have hunted in temps of -20C/-4F and colder for long periods, and have never had a problem. What does happen however, is that screen on the machines gets a little fainter, and there is a lag time for readings as you move your coil over a target. If you use any machines with variable tuning knobs, they tend to stiffen up. The coil wires also stiffen up, and could possibly break by the coil or connector by the electronics box. You just have to be real careful when hunting in the cold. I too was warned many years ago that there could be some damage, and to use the machine in temperatures as "operating temperatures" stated in the manual. This could void the warranty. I started using a GTA 500 after the warranty expired, as I was willing to pay for any damages. But that never happened.
I mostly use my ACE 250 in the cold, as I can cover the batteries with a hand warmer, wrap the electronics box with a wool sock, and the machine works just like it would on a hot day.
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