In the 1.23.1 release of Ingress we were treated to a new item among other things; Power Cubes.
So what is a Power Cube and What will it do for me?
It appears they are XM storage units. and there are 8 levels of power cubes. The higher the level the greater the storage.
What I do not know yet, but am assuming, is that they work like XMP Bursters and you can not use Power Cubes greater than your player level.
How do I find Power Cubes?
They are an item you get when you hack a portal, much like XMP Bursters, Portal Shields, etc...
Get out there and find some Power Cubes!