The transition from lead-acid to lithium-ion is forcing forklift OEMs to completely redesign the chassis, and not just for weight savings. A lead-acid battery is a massive, dense block of lead and acid sitting low in the frame; it acts as a heavy, dampening ballast. A lithium-ion battery is often half the weight and much smaller for the same kWh output.
To maintain the truck's rated capacity, the counterweight must be redesigned, but there is a more insidious engineering challenge: structural rigidity. On many medium-capacity forklifts, the lead-acid battery sits in a well between the drive axle and the mast. The battery itself is so heavy and tightly fitted that it acts as a structural cross-member, preventing the chassis rails from twisting under load.
When you remove that 3,000-pound lead block and drop in an 800-pound lithium pack, the chassis loses its structural support. When the operator lifts a heavy load at full forward reach, the mast torque can actually twist the frame rails slightly. Over thousands of cycles, this fatigue cracks the welds on the battery compartment and can misalign the drive axle. Modern lithium forklifts are being designed with heavy structural steel cradles that bolt the lithium battery solidly to the frame, essentially using the battery housing as a stressed member to replace the rigidity lost by the missing lead.
