I got the Enphase battery system finally up and running. I can configure it in a few different ways. The default setup is to take extra power from solar generation (during the day) and store that in the batteries and use it at night to power the house. You can configure how far down you want to let the batteries go in that scenario.

You can use the batteries for time of use offsets if you have variable time of day billing. If power is more expensive in the middle of the day but cheaper at night you can have the batteries charge at night and provide power during the day.

You can also configure them for emergency backup, and have them stay at 100% charge in case the power goes out. If there is a severe weather alert they automatically switch to backup mode until the event passes.

Lastly, and perhaps the most valuable, is the ability to integrate with a generator so when you are off-grid you can have the generator auto start and stop based on the battery level, which significantly extends the generator/battery lifecycle.

I tested the grid failure mode and it is very fast. I could not detect the switchover, and my inline conversion UPS did not trip during the transition. Good engineering on that part to go from Grid-NoGrid-Grid including synchronization without a hitch.