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.

Serve as Mainspring’s technical lead for battery pack and module design.

Partner with battery suppliers to review, improve, and influence pack and module architectures.

Own battery hardware from requirements definition through production launch and sustaining engineering.

Evaluate battery designs for safety, reliability, manufacturability, thermal performance, lifecycle, and cost.

Lead technical reviews of cell integration, interconnect systems, thermal solutions, and safety features.

Support supplier selection, design reviews, validation activities, and manufacturing readiness.

Develop battery architectures for future generator platforms.

Collaborate with Electrical Engineering, BMS, Reliability, Manufacturing, Test, NPI, and Supply Chain teams.

Lead root-cause investigations and corrective actions for production, test, and field issues.

Provide technical leadership on complex battery-related challenges.

Travel to supplier sites as needed to support development and issue resolution.

BS or MS in Mechanical Engineering or a related discipline.

10+ years of engineering experience with significant focus on lithium-ion battery pack or module design.

Deep understanding of battery pack and module architecture.

Experience working directly with battery suppliers and contract manufacturers.

Strong knowledge of cell integration and interconnect design, including bus bars, current collectors, voltage sensing, harnessing, and cell terminal joining methods.

Experience designing series and parallel battery architectures.

Working knowledge of cell construction, dielectrics, fusing, compression systems, and thermal interface materials.

Experience with battery thermal management and thermal runaway propagation mitigation.

Understanding of battery aging, lifecycle performance, and charge/discharge behavior.

Knowledge of environmental durability, vibration, grounding, creepage/clearance, and EMI-related packaging requirements.

Experience supporting validation testing, manufacturing launch, and sustaining engineering.

Experience with UL certification of battery systems.

Proficiency with SolidWorks and PLM systems.

Experience with prismatic-cell battery systems.

Knowledge of BMS integration, contactors, relays, and protection systems.

Experience with high-voltage battery or power systems.

Experience with battery thermal protection materials and thermal interface design.

Familiarity with FEA tools such as Ansys.

Experience with products deployed in harsh outdoor environments.

Background in EVs, energy storage systems, industrial electrification, power electronics, or other ruggedized energy platforms.

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