I think you've probably gotten your answer, but is this a digital, smart, or... (I can't think of what the other kind is called.)? I had a thermometer that was doing the same thing, and I was thinking when the time change came, it'd be more accurate but nope, it changed with the time change and still had the same issue. I'm not sure exactly what was the issue (this was a digital, not a smart thermometer), or when the issue started, but at some point, the rechargeable (Energizer AA) batteries eroded which resulted in them not being able to recharge, so eventually I replaced the thermometer because I didn't want to risk ruining other batteries by putting them in.