Electric dolly converts diesel truck to hybrid and cuts 85% of emissions

The electrification of heavy fleets often comes up against the price of electric trucks, which cost double or triple that of a diesel equivalent, in addition to suffering from limited autonomy and lengthy recharges. To get around the obstacle without changing the entire fleet, the San Francisco-based startup Revoy created a self-propelled electric dolly that is coupled between the tractor and the semi-trailer — and promises to cut up to 85% of carbon dioxide emissions without touching the engine.

The company received authorization from NHTSA, the American road safety agency, in 2023, and completed a one-year pilot with carrier Ryder in 2024. The first commercial operation begins later this year on a 322-kilometer stretch near Portland, Oregon, with four units assembled from Chinese components.

How the battery on wheels works

With 3.96 meters in length and 9.9 tons, the equipment carries a 575 kWh lithium iron phosphate (LFP) battery — a capacity equivalent to that of a complete electric truck — which powers its own motorized axle. When the driver accelerates, the system identifies the load demand and takes over part of the traction effort, relieving the diesel engine. When braking, it operates in regenerative mode to recharge the batteries, an effect that according to Revoy reduces the stopping distance by up to 30%.

With a total gross weight of 36.3 tons, the set runs more than 322 km in electric mode alone. The installation does not require modification to the truck or trailer, and the module features active systems against rollover and knife effect.

The promised gains are significant. According to the company, the average consumption of a heavy truck goes from a range between 29.4 and 39.2 liters per 100 km to somewhere between 6.7 and 11.8 liters per 100 km, and can reach 5.9 liters per 100 km on routes of up to 241 km. According to CEO Peter Reinhardt, fuel accounts for more than a fifth of a trucker’s operating costs, and U.S. retail diesel remains about 40% above the level of $3.80 per gallon before the current conflict in the Middle East.

Subscription per round mile

To avoid vehicle downtime during prolonged recharges, Revoy bets on quick changeover: at bases along highways, the unloaded module is replaced by a full one in less than five minutes. The hardware is not sold: Revoy retains ownership of the dollies and charges the fleet owner a subscription per mile driven.

The potential market explains the interest of investors: the United States has 3 million registered heavy trucks, responsible for 6.7% of all greenhouse gases in the country. Revoy has just raised US$ 27 million, bringing the total raised to US$ 41 million, and will develop a second generation of the dolly, cheaper and with a smaller battery, but with equivalent autonomy – with the goal of having dozens of units on American routes by the end of 2027.