Well, they may invent something that only weighs 30 pounds, and stores 50KW-hrs of energy, but it won't be a battery. The best you could hope for is a fuel cell that works off liquids.
Batteries have progressed slowly. Lead acid is still in high use. But, some new technologies such as lead coated carbon pick up, batteries have a lot of promise, to half the weight of lead acid's in cars.
Lithium Sulfur promises to half the weight of LiPo Lithium Polymer batteries. But past that, I don't think their is a element that can store more charge per low atomic number.
Even then, were talking about at least 200 pounds of batteries, and more like 400 pounds, at best.
Here's a nice picture of battery progression. You could make the argument that we've 5X'ed battery energy per weight, but I believe it's only due to moving straight to the lightest element known.