Getting a little deeper in to Solar power, and was wondering about something. It's sort of like a UPS, but in reverse I guess. I'd like to run off the batteries as much as I can, but don't want to get cut off in the middle of something. Was wondering if there is a device or circuit, that would switch to grid power, when the batteries get low. Would like it to be a smooth switch over, like the USP on my computer. There must be something like this out there, just don't what to call it, so searching has been much help yet.