I've toyed with the idea of lithium ion for UPS or solar power, but not sure if I'd feel comfortable having those in my house. Even "professional" devices blow up a lot. If they have problems, then something I build myself is probably even more at risk than something that's gone through tons of R&D, ULC, CSA, ETL etc.
The nice thing with lead acid is you can just float them indefinitely and don't need to worry too much about regulating how much voltage they get.