They have them, they are called inverter-chargers. I recommend Victron or Magnum for quality with UPS grade switchover. I keep wanting to do a Victron 3000 12v

They have them, they are called inverter-chargers. I recommend Victron or Magnum for quality with UPS grade switchover. I keep wanting to do a Victron 3000 12v for a critical loads in my house (fridge, lights, outlets) to use with some spare 6V lead acids I have I took out of my RV when I switched it to LFP. In the future I could switch the batteries out for LFP if I wanted. If building from scratch I would probably do a 48v rack style LFP with 48v inverter instead again probably Victron, wish they would make a rack mount version.