Staff Mechanical Engineer - Battery Design

Mainspring Energy•Menlo Park, CA

7h•Onsite

About The Position

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. 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. Battery systems are a critical part of Mainspring’s linear generator platform, supporting startup, transient load management, and overall system performance in demanding real-world environments. This role offers the opportunity to solve complex battery engineering challenges, drive supplier strategy, and shape future energy products deployed at scale. 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.

Requirements

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.

Nice To Haves

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.

Responsibilities

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.