San Francisco startup Revoy has developed a swappable electric dolly that instantly transforms existing diesel semi-trucks into efficient hybrids by connecting directly between the tractor and trailer. This massive 575 kWh "battery on wheels" tackles the heavy lifting to slash emissions by up to 85% and improve fuel economy, allowing drivers to swap depleted units for charged ones at highway hubs in under five minutes. Offered through a per-mile subscription, it gives fleet operators a cost-effective way to decarbonize without buying entirely new electric rigs.