Nikola Corp. announced a long-term supply agreement with Proterra Inc. for battery technology, giving the electric big-rig maker a second source for the critical components.

Burlingame, California-based Proterra will start delivering prototype systems to Nikola next quarter, with full production of trucks using Proterra’s battery packs starting in the fourth quarter, the companies said Tuesday in a statement. The technology will also be used for hydrogen-fuel-cell electric trucks, which are due to go in to production in the second half of 2023.

The agreement bolsters the supply chain for embattled startup Nikola, whose road to production of battery-electric and fuel-cell semi trucks has been plagued by challenges. Phoenix-based Nikola has previously disclosed Romeo Power Inc. as a pack supplier and discussed working with multiple cell suppliers, without disclosing their names.