ewest:
When you say you have an older one that is good, just how old? Reason for asking is because I have 2 of them, both purchased in early Spring of 2007. I'm trying to figure out if I have good ones or bad ones. One I put into service relatively quickly, the other one is still in the garage. I noticed that the solar panel wouldn't keep the battery up, and I ended up hooking up a much larger panel (2' x 4' like the ones that you see on the highway "warning construction ahead signs") to it, but it still wore down the battery quickly. I have the timer to feed 2x day, 15 seconds each time. I thought it was because it is in partial shade, then I thought the battery was going bad (2nd year of use).
I'm going to switch to Aquamax 500 this year and see how it performs vs. the generic food from the farm supply store.