When engineers working for the Swiss Federal Railways (SBB) have some welding to do out on a section of track, they don’t have to fire up a diesel generator anymore. They can plug their tools into a portable battery instead. A silent, emissions-free battery that can also power lights and measuring instruments.  The SBB now has around 80 batteries made by Instagrid, a fast-growing startup headquartered in Germany. Welding requires a significant burst of energy so the batteries have to come with a kick.  “That is what we are specifically good at, the power density,” asserts Andreas Sedlmayr, co-founder and…This story continues at The Next Web