Investors have been concerned about slowing growth in electric vehicle (EV) sales. One reason is the lack of charging infrastructure. But battery maker Solid Power (SLDP 4.27%) is one of several companies that hopes to have a long-term solution.

Solid Power shares popped today after fellow solid-state battery maker QuantumScape (QS 5.69%) announced some game-changing news. As of 2:45 p.m. ET, Solid Power shares were higher by 11.2%.

Ending range anxiety

That move was dwarfed, however, by the 47% spike in QuantumScape shares at that time. The stock was soaring after a battery unit of partner and potential customer Volkswagen Group said tests confirmed that the solid-state battery technology it is testing for QuantumScape achieved more than 1,000 charging cycles without losing virtually any charging capacity.

That equates to over 300,000 miles an electric car could travel without losing any battery range. With most existing EVs having a range of 250 to 300 miles, many consumers have remained shy of transitioning to an EV for fear of running low without a place to charge. Solid-state technology could be the answer, and Volkswagen's PowerCo unit's confirmation of that performance -- at least in a laboratory test setting -- has investors piling into names in that sector today.

Not there yet

That helps explain why competitor Solid Power's stock popped today too. But even QuantumScape doesn't expect to be able to commercialize its technology for about two more years. Solid Power has partnered with BMW for testing but doesn't expect to be able to scale its battery cells to a high-volume production level until 2028.

Those lengthy timelines are why even speculative investors have sold shares in these stocks over the past year. But both Solid Power and QuantumScape have sufficient liquidity to continue to have automakers testing the technology.

If solid-state batteries are able to extinguish range anxiety, there will be plenty of upsides for shares of both Solid Power and QuantumScape. That's a big "if" though, so  any investment should be considered completely speculative, even after today's positive gains.