I didn't know about NiFe batteries. With a long lifetime, deep discharge durability, and cheap non-toxic construction they look quite promising. Except overall

I didn't know about NiFe batteries. With a long lifetime, deep discharge durability, and cheap non-toxic construction they look quite promising. Except overall efficiency isn't great, and it looks like they require regular maintenance. Of course, maintenance becomes less of a problem at neighborhood/grid-local scale.