I just have battery/usb air pumps. My reef survived 8 days without power with just aeration after a hurricane. They received aeration for about 8 hours per day (they had to share with some other tanks). I lost one frag that was struggling before then, but everything else did just fine.
Flow is a big part of it. My pump made a decent airlift in the tank.
We are still getting utilities back up in my area from Laura. I never consider tap water part of a system failure. Temps inside the house were around 100, tank is evaporating like crazy and guess what. You don't have running water. Then 2-3 days later when water comes on it is brown and barely any pressure. Surely not enough to push through a RO/DI membrane. Batteries will drain, fuel for your generator will go dry. This hobby is a luxury.
Build my own battery back up for my MP40. However, would like to have something for extended power outages that would require some level of additional life support (e.g. running heaters, return pump, etc.)
We have an Ecotech backup that I swap out the SLA on every couple years. We also had an expensive UPS with part of the tank connected until we had an actual power outage and it only lasted about 10 minutes. What a waste of money!
For extended outages we have a propane generator for the fish tank, refrigerators, etc. We're also in the process of doing a major upgrade to our 12 year old Tesla (used to be Solar City) photovoltaic system which will triple the size and include a couple power walls. Assuming sunny days, it should keep us powered indefinitely.
Never found battery back ups to be to reliable so I bought a genarator to power the entire house. Actually considering replacing the gasoline carb and converting it to propane and have a 100 gallon tank.
We have whole house battery backup with 2 Tesla Powerwalls. Highly recommend to anyone considering solar systems or looking into buying a generator. They are still eligible for a generous federal tax credit.
I have 4x Ecotech batteries, one for each of two MP40s, and two for one of my 2 Vectra M2 return pumps. These can power the Sump and circulation for just over a day and a half.
I also have 3 AC UPSs. Each of my 2 Apex 832 power bars plug into their own, and all other devices that are not on the Apex plug into the other. With programmed off timers in the Apex to turn off many of the outlets after a few minutes, the rest of the devices can run for several hours to handle most temporary power cuts.
Still looking into a whole-house generator to handle longer power issues...like hurricanes and floods, which we get regularly in coastal Texas...