Hot weather in car

I have a 5th gen (enhanced) iPod Classic on which I've replaced the hard drive with a Tarkan iFlash-Dual and keep in my car front seat compartment connected to the car audio system. It worked fine all spring until recently when we started getting temps over 80 - now when I start the car, it says there's no iPod until I open the compartment and press the middle button. Thinking it might be the battery, I just replaced that with one from iFixit but it did the same thing today, even in the morning when it was cooler.

Any ideas?