Remember that average use does include giant section of the night when nobody's doing anything. So your average daytime use is likely higher than your average overall, especially for anything like stove, HVAC, water heater, dryer More on reddit.com

You need to identify your power consumption during the peak rate time you want to avoid. This will define the storage capacity of your battery system Also identify the circuits that will be powered by battery. This will determine size of your inverter. (For example: air conditioning, water heater, electric range. But not dishwasher, cloths dryer or cloths washer, etc because will not use during peak times More on reddit.com

Yes they work the same way and can backfeed into the panel using an interlock or transfer switch. Depending on how long you want to cover it gets expensive really quick. Some people set batteries up for Time of Use allowing to save $ by using the batteries to power their house during peak hours, though this usually requires an agreement with your utility provider. You can also do a hybrid, buy a battery that last for normal outages, 12-24hrs, then use a gas generator to recharge for longer outages. The key to efficient battery backup systems is to first figure out what circuits and appliances are critical and ideally isolate them using a transfer switch. Unless you got big bucks, then go for a huge battery system, if you’re in the US, you’ve got a week left to install it to qualify for a 30% tax credit. More on reddit.com

energy capacity is power over time. 60vdc * 5amphour = 300 watt-hours. inverters are pretty efficient. most are well above 85%. yours will have a spec. lets assume 85% efficiency. 300wh * 0.85% = 255wh. so your battery can probably power a 250w load for an hour. or a 25w load for 10 hours. More on reddit.com