What happens when transportation infrastructure can’t handle heavier batteries?  

Larger, heavier energy storage systems are becoming the new norm. But they’re also a transit liability.  

“The battery energy industry has gotten ahead of its skis in terms of optimizing these containers for high energy density at the expense of heavier containers,” explained Daniel Finn-Foley, the director of energy storage and market intelligence at Clean Energy Associates.  

He told ESS News that while 3-4 megawatt-hour batteries usually weigh under 40,000 kilograms, five MWh batteries weigh closer to 40,000-45,000 kilograms, or nearly 50 U.S. tons. According to Finn-Foley, that’s the inflection point for major weight distribution issues.   

“40 tons is generally the limit for standard trailers you see on the road in the United States,” he said. 

It can be difficult to find drivers and trucks capable of managing such large loads, Finn-Foley explained. Shipping companies are still “catching up” and learning how to move the heavy systems around without risking tip-overs. Coupled with added permitting requirements, heavier BESS drive up costs and deployment timelines.  

“The bigger problem is when you have a 40+ ton truck moving over aging American infrastructure,” Finn-Foley said, highlighting how the friction doesn’t stop once batteries are en route.  

Generally speaking, it’s easier to build BESS further away from city centers. But, he said, “That’s also where the infrastructure gets older and more rickety, which adds complexity and makes deliveries even more challenging when you have a 45-ton battery that needs to go over a bridge in rural Texas with a 20-ton weight limit.”  

Still, a second, less visible barrier is making things worse: fragmented interstate logistics policy.  

“Luckily, a lot of BESS transportation will be on federally regulated interstates,” Finn-Foley said, adding that state-level regulations could throw a wrench in the works. He explained that the vast majority of BESS containers are shipped through major ports in states with 40-ton weight limits like California and South Carolina. While many states like Florida and Michigan allow up to 70-ton loads on their roads, the patchwork of state regulations imposes a de facto weight limit of 40 tons.  

“If you have a system above 40 tons, where are you going to put it where you can actually drive it around?” Finn-Foley said. “Systems are reaching the port of Los Angeles, but the demand is in Texas, Arizona and growing in the Midwest. There is no clear corridor to get the batteries there if you have a system weighing 50 tons or more.” 

That’s why the 40-ton threshold is a critical tipping point for deployment.  

“That is the breakpoint where you don’t need special permitting,” Finn-Foley stressed. “Weight is becoming a bottleneck more than energy density.” 

Manufacturers are starting to adapt. Chinese manufacturer CATL recently launched a 9 MWh two-in-one stackable ESS; the two 20-foot containers each weigh 36 tons. This complies with transit weight restrictions in most global markets while still providing high energy capacity. 

“This is the first signal the industry is adapting to these weight constraints,” Finn-Foley said, explaining it was so focused on improving container-level energy density and maximizing efficiency that it hit the weight bottleneck “without realizing.”