A new kit approved by the California Air Resources Board (CARB) lets fleets turn their F-150 pickups into plug-in hybrids.

The XL hybrids plug-in system is sold as an upfit for the truck. Intended for fleet customers, the system is installed by certified installers. Currently, XL Hybrids does not sell to consumers.

XL offers plug-in hybrid kits for multiple commercial vehicles including the Ford Superduty, Ford Transit, Chevy Express, and even the chassis used to build shuttle buses and delivery trucks. The company’s latest kit is for the best selling vehicle in America, the Ford F-150 pickup.

XL has just announced that their F-150 kit has won a California Air Resources Board executive order approval. That means that the kit has been certified for sale in the state and that it passes emissions testing.

The XL hybrid kit isn’t sold as a ready to go truck, it’s sold separately as a kit. Intended for fleet customers, it needs to be installed by certified installers.

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The kit uses a 15-kWh lithium-ion battery and adds regenerative braking to charge it back up. The electric motor goes in the middle of the drivetrain, mounted inline with the driveshaft.

XL says that it offers a miles per gallon improvement of up to 50 percent, and the system has a three year, 75,000-mile warranty. It’s intended for 2.7 and 3.3-liter V6 equipped F-150 trucks in two and four-wheel drive.

XL Hybrids recently announced that it would be adding hybrid drivetrains to 234 of Verizon’s Chevy Express 2500 work vans to help that fleet increase fuel economy and lower emissions.