It is not safe to open a lithium battery, inside of a cell phone "motorla something". What would that imply? "open the battery" does it mean un-soldering the cells or what? (I'm trying to understand what exactly he's planing NOT to do).

Batteries contain various hazardous materials and are usually "sealed" so that the internal materials (the hazardous ones) will not be encountered with normal use.

But breaching that external barrier can expose you to those chemicals with possibly tragic effects.

So, "Don't open that battery."