A friend was building up a 24V power wall using old laptop battery cells, don't think he ever finished it, needed hundreds of cells, having to sort them out first to even up capacity, then join them into a bank with individual battery fuses. Can understand doing this for something like a push bike power pack, but for a stand alone "Power Wall" its a huge amount of effort.
I currently require a portable inverter device to replace an old petrol AC generator; decided to use the small 50 AH Lifepo4 cells as a power source, these will be safer and much easier to build.
See link here where I have started on the project.
http://www.thebackshed.com/forum/Vie...ID=4&TID=14660
Cheers
Mike