Craig,
Leaving a battery plugged in can do that. Sounds like there is a parasitic draw somewhere. For what it's worth, I use di-electric grease on all my non-soldered plug-and-play electrical connections. So far so good.
Oh, and welcome to the forum. 'AC'
Welcome, hope you get your Kooties under control. What? Corrosion? I thought you said Kooties, well never mind, I would also give the di electric grease a try.