Good point Vic, I hadn't considered the effect of long term humidity on the autofeeder...

Just so you don't get the idea that humidity is always a problem, the other two feeders that are above the glass and drop through a hole, have no humidity problems at all. I've had food in them for months at a time without any clumping.

My tank has a canopy over it which the feeder would have to be inside of. I did run it for a week at Christmas without issue, but wasn't confident that it actually did anything for the fish. The feeder I have does have an "anti humidity door" on it, but the battery connections corroding isn't something that I had considered. I think the best thing to do is to just set it up and let it run for a couple of weeks before I leave and see how things do.