Staff Mechanical Engineer - Battery Design

About Mainspring

Mainspring Energy manufactures and delivers fuel-flexible, low-emissions local power solutions that rapidly add new capacity and deliver reliable, affordable, and sustainable electric power. The company began commercial shipments of its Mainspring Linear Generators in 2020 and today has hundreds of megawatts in advanced development and field operations for leading Fortune 500 companies, data centers, and utilities. Mainspring also partners with global energy leaders including AEP, NextEra Energy Resources, Schneider Electric, and more. The core values that ground our work, guide our decisions, and connect us together: Pragmatic Optimism Excellence without Ego Proactive Collaboration

About the Role

Mainspring Energy is seeking a Staff Mechanical Engineer – Battery Design to lead battery pack and module development for current and future energy platforms. As Mainspring's internal battery technical authority, you will help define next-generation battery architectures for future products while improving systems already in production. You'll partner closely with battery suppliers to influence pack and module designs and drive solutions that balance safety, reliability, manufacturability, performance, and cost. You'll influence key decisions across cell integration, thermal management, safety, and system architecture while working at the intersection of mechanical, electrical, and battery engineering. Our battery systems do far more than just store energy. They are the dynamic core of our linear generator platform. Tightly integrated into every sub-system, they act as the ultimate performance driver—sparking to life during grid-islanded startups, taming dynamic transient loads, and delivering resilient long-duration standby. This role is your chance to tackle complex battery engineering challenges head-on, drive our supplier strategy, and ensure our systems deliver rock-solid, scalable reliability in the real world. The ideal candidate combines deep lithium-ion battery pack expertise with strong supplier-management experience and the ability to translate system requirements into robust production-ready designs.