I agree with OP if your timeline is the next few years, but there is still a ton of headroom between, say, lithium polymer and the theoretical maximum for speci

I agree with OP if your timeline is the next few years, but there is still a ton of headroom between, say, lithium polymer and the theoretical maximum for specific energy (the speed of light squared). Obviously nuclear batteries are going to be a long time coming (I'm not even aware of any theoretical way to make, say, a fission reaction release electrical rather than thermal energy), but if you expand on the definition of "battery" a bit from something you just plug in to recharge to something that maybe requires being physically swapped out and reprocessed, there are some very promising avenues of research. The one I'm most excited about is the vanadium boride-air cell, which has a practical energy density on par with diesel fuel. The catch is that is likely impractical to make one that can be recharged by simply reversing the current through it, so it would require a network of reprocessing plants and battery-exchange facilities.