If we're talking electric, it is my pleasure to point out that storage batteries, in my opinion, are presenting no problem at all. There are much less environmentally destructive ways to store energy that present no technological unknowns to be solved. If we use energy to charge a storage battery, that energy will dissipate while it erodes the storage capacity. If we use that energy we are producing to pump air into a tank, flex humongous springs, compress any of a number of resilient substances, that energy can be retained with comparatively little, if any loss or detriment to the future energy holding capacity. If the energy is to be retained at a static location, the practical storage devices are expanded to include any kind of mass that can be lifted, such as water in an elevated tank, a boulder, or concrete block. These storage devices are mostly organic and harmless to the environment when failure does occur, the technology has been exhaustively researched and electric storage batteries present hazards besides weight. Electrocution, fire and explosion. There are already automobiles on the road that are propelled by compressed air, reportedly with high performance, good efficiency and safety. A spring can snap and a tank can explode, but neither can electrocute or chemically burn or pollute, and exploding batteries have killed drivers.