The promise of lithium-ion forklifts in freezer operations (-20°F to -30°F) is that they don't suffer the severe capacity drop that lead-acid batteries do. However, the physics of lithium chemistry still demands a minimum temperature to charge safely. If you charge a frozen lithium cell, the lithium ions plate onto the anode instead of intercalating, forming sharp metallic dendrites that pierce the separator and cause a dead short.
To prevent this, Li-ion batteries have built-in heaters. When the truck is parked and plugged in, the Battery Management System (BMS) activates resistive heating pads to warm the battery core to at least 32°F before allowing the charge cycle to begin.
The problem is the parasitic drain. Warming a 2,000-pound mass of steel and lithium from -20°F to 32°F requires a massive amount of energy. In multi-shift operations, a truck might only be plugged in for 45 minutes during a break. The heaters consume 80% of that energy just to reach charging temperature, leaving very little time to actually put amp-hours back into the pack. Facilities are finding that Li-ion trucks parked in the deep freeze overnight are arriving at the start of the shift with a lower state of charge than when they were parked, because the heaters ran all night trying to keep the battery warm. The solution requires expensive "warm rooms" at the dock where trucks can be parked at 50°F, completely negating the convenience of drop-in charging.
