Mercedes EQS Tests Revolutionary Solid-State Battery For 621-Mile Range

Solid-state batteries are promising better safety and higher energy density than traditional lithium-ion packs. That's why Mercedes has officially begun road-testing a “slightly modified” EQS fitted with a lithium-metal solid-state battery.

The test vehicle is using cells from Factorial Energy and features a floating cell carrier designed to handle expansion and contraction during charging and discharging.

Unlike conventional EV batteries, this one uses a solid electrolyte instead of a liquid, improving safety and enabling the use of lithium-metal anodes. The result? A potential energy density of up to 450 Wh/kg—meaning lighter, more compact batteries with longer range.

For the Mercedes EQS, that translates to a whopping 621 miles on a single charge—about 25% more than a similarly sized lithium-ion pack. For comparison, the standard EQS 450+ with a 118 kWh battery offers around 497 miles under the WLTP cycle.

Mercedes will put the prototype through rigorous testing over the next few months, but Factorial Energy’s CEO, Siyu Huang, is already calling this a historic moment, proving that solid-state batteries are no longer just a lab experiment. Mercedes’ CTO, Markus Schäfer, sees it as a major step toward innovation and sustainability, hinting that we might be closer than ever to seeing solid-state tech in mass-market EVs.