While the world is racing to commercialize humanoid robots to realize unmanned factories, batteries remain a core challenge that has yet to be easily resolved. Given that at least 4-5 hours of continuous operation is essential to substitute real labor at industrial sites, advances in robot charging and battery technology are urgently needed, industry observers say.
According to the robotics industry on the 20th, even the most advanced humanoid robots on the market can perform actual work for only 1-2 hours on a full charge. The cause of humanoid robots' early discharge stems from complex physical and electrical mechanisms that differ fundamentally from those of ordinary industrial robots or electric vehicles.
According to a paper titled "Powering Humanoid Robots: The Central Role of Battery Technology," published in late March this year in the international journal The Innovation, a standard humanoid robot weighing about 70 kg is allowed only 5-8 kg of battery pack weight to maintain natural bipedal walking and dynamic agility. If a heavy battery is installed indiscriminately to expand capacity, the robot's center of gravity collapses, walking stability deteriorates, and joint motors consume more power to bear the added load — a "weight paradox." In other words, the more battery added, the faster the discharge — a built-in dilemma.
Deng Zhaozhao, a professor at Shenzhen University in China and author of the paper, said, "For humanoid robots to overcome the battery weight constraint and secure practical operating time, cell technology with an energy density of at least 350 Wh per kg is essential." However, current commercial lithium-ion batteries offer cell energy density of only about 250-300 Wh per kg. Moreover, the actual system-level energy density inside the robot — including the battery management system (BMS), cooling devices, and protective components — is much lower. Because non-standardized batteries must be squeezed into limited body space, dead space arises and output efficiency declines.
The extreme volatility of output load can also cause battery failures. Unlike industrial robots with fixed robotic arms, humanoid robots must continuously fine-tune dozens of joint motors to maintain balance in human environments. In particular, when a robot lifts heavy objects, climbs stairs, or exerts instantaneous restoring force to avoid falling from external impact, the battery's discharge rate surges momentarily.
To overcome these limits, academia and industry are turning to next-generation batteries. Lithium metal and lithium-sulfur batteries are being studied as alternatives to push beyond the limits of lithium-ion batteries. Lithium-sulfur batteries in particular are evaluated as optimal for lightweight robots, with theoretical energy density several times that of lithium-ion cells and lightweight sulfur as a cathode material. However, low cycle life and charge-discharge efficiency remain challenges. Many believe that solid-state batteries — which maximize safety and energy density by using solid electrolytes instead of liquid ones — will ultimately be the key technology determining the spread of humanoid robots.
According to market research firm SNE Research, the global humanoid robot battery market is projected to reach only 1.37 GWh even by 2030. However, by 2040, it is expected to grow explosively to 138 GWh. The forecast is that solid-state batteries will become mainstream starting around 2030.
