Flex Battery Testing Jobs in California (NOW HIRING)

Battery / Pack Systems Engineer – Integrated Rack Power Platform

Location: San Jose, CA (On-site)

Reports To: Head of Engineering, Data Center Power Platform

About the Role

We are building an integrated PSU + BBU rack power shelf that combines power conversion and solid-state battery backup into a single high-density platform for hyperscale AI data centers.

This product replaces traditional separate PSU and BBU shelves with a unified architecture that leverages the unique safety and performance characteristics of solid-state battery cells.

As the Battery / Pack Systems Engineer, you will own everything from cell to pack—including mechanical integration, Battery Management System (BMS) architecture, thermal management of the battery section, charge/discharge optimization, safety engineering, and cycle life validation. You will serve as the critical bridge between our cell technology and the power platform, translating evolving cell-level specifications into robust pack-level designs in near real-time.

What You'll Do

Design the complete cell-to-pack mechanical assembly, including:

Cell stacking

Compression systems

Electrical interconnects (wire bonding, busbar welding, or flex circuits)

Structural integration within the shared PSU + BBU enclosure

Architect the Battery Management System (BMS) hardware topology, including:

Distributed versus centralized sensing

Passive versus active balancing

Protection FET sizing

Sense line routing

Communication interfaces

Develop and tune State-of-Charge (SOC) and State-of-Health (SOH) estimation algorithms using:

Coulomb counting

Extended Kalman filtering

Impedance-based estimation methods

Solid-state battery electrochemistry models

Co-develop charge and discharge profiles with Firmware Engineering, including:

CC-CV charging curves

Temperature-dependent charge rate limits

Fast-charge protocols

Float and maintenance charging strategies optimized for data center duty cycles

Design thermal interfaces between battery cells and the enclosure using:

Thermal pads

Gap fillers

Heat spreaders

Dedicated thermal pathways

Collaborate closely with the Thermal / Mechanical Engineering team.

Conduct pack-level FMEA and battery safety analysis.

Define and execute abuse testing protocols including:

Nail penetration

Crush testing

Overcharge testing

External short-circuit testing

Validation adapted specifically for solid-state battery behavior

Develop accelerated aging and life-cycle validation protocols for data center applications, including prolonged high-State-of-Charge float conditions with infrequent high-power discharge events.

Serve as the primary liaison with the cell development team, translating pack-level requirements into cell-level specifications and feeding laboratory and field performance data back into future cell development.

Support safety certification efforts including:

UL 1973

UL 9540A

What You Bring

Required Qualifications

8+ years of experience designing battery packs or battery modules, with at least one product successfully validated through prototype testing or production.

Hands-on Battery Management System (BMS) architecture experience. (PCB layout experience is not required, but the ability to define system topology and component selection is essential.)

Strong battery characterization and modeling experience, including:

Impedance spectroscopy

Capacity fade analysis

Thermal characterization

Experience with battery safety standards, particularly:

UL 1973

Exposure to UL 9540A strongly preferred

Proficiency in pack-level mechanical and thermal design using:

SolidWorks

Creo

Equivalent CAD platforms

Thermal simulation experience is a plus.

Comfortable making engineering decisions while working with evolving battery cell specifications and incomplete technical data.

Preferred Qualifications

Experience with solid-state, lithium-metal, or other next-generation battery chemistries, including research environments.

Experience designing battery systems for:

Data centers

Telecom backup power

Stationary energy storage

Understanding of float-then-discharge duty cycles compared to electric vehicle cycling.

Familiarity with electrochemical modeling tools such as:

COMSOL

PyBaMM

AutoLion

Equivalent platforms

Experience with IEC 62619 industrial battery safety standards.

Applications engineering experience at a battery cell manufacturer, translating cell performance into production pack designs.

Knowledge of functional safety principles including:

IEC 61508

Equivalent standards

Why This Role Matters

You sit at the center of the engineering organization. The Power Electronics Lead depends on your voltage windows, current limits, and battery performance requirements. The Firmware Engineer relies on your Battery Management System algorithms and protection strategies. The Thermal / Mechanical Engineer depends on your cell thermal requirements and packaging constraints. The Cell Development Team relies on your pack-level feedback to continuously improve cell performance.

Most importantly, the safety, reliability, and long-term longevity of solid-state batteries deployed in hyperscale AI data center racks will ultimately be defined by your engineering decisions. This role is central to delivering the core technology differentiator of the entire platform.