ON.energy is setting the standard for large load interconnection. ON’s patented AI UPS™ is a medium-voltage UPS that serves as a firewall, protecting the data center from the grid, and the grid from the data center. With multiple gigawatts currently under construction, we are enabling grid-safe data centers. 

Principal Battery Systems Engineer 

Role Overview 

We're looking for a Principal Engineer to set the technical direction for our BESS product line and to own the product roadmap across multiple concurrent development cycles. This is the senior technical voice on the product team: you'll architect new products, resolve the hardest engineering trade-offs, set the engineering standards others work to, and represent ON.energy's product engineering externally — to vendors, customers, certifying bodies, and the broader industry. You should be comfortable operating with minimal direction, holding the bar on technical quality, and moving multiple product cycles forward in parallel without losing the thread on any of them. 

What You'll Own 

Architecture & Technical Direction 

• Set the architecture for the BESS product line and own the technical roadmap across multiple concurrent product cycles. 

• Make the hard trade-off calls — cost vs reliability, performance vs lead time, standardization vs customization — and document the reasoning so future decisions inherit context. 

• Define the engineering standards, design rules, and review gates that other engineers on the team work to. Own the product-engineering bar. 

• Approve major design changes; act as the final technical authority on the change baseline. 

Multi-Product Development 

• Run multiple product development cycles in parallel — concept through prototype, FAT, field deployment, and revision — without losing depth on any of them. 

• Drive cycle cadence: decide what ships when, where the technical risk lives, what gets parallelized vs sequenced. 

• Identify and execute the next-generation product moves — higher voltage class, alternate chemistries, new form factors — ahead of customer demand. 

Detailed Engineering Depth 

• Personally own the hardest pieces of work: novel architectures, first-of-kind designs, advanced component sizing (fuse coordination, busbar thermal optimization, protection coordination across cascaded systems), cabinet thermal modeling, and complex protection schemes. 

• Review and approve detailed engineering drawings — SLDs, GAs, schematics, panel layouts — at the level required to sign off, not just consult. 

Vendor & Supply Chain Strategy 

• Own the strategic relationships with key vendors — battery, PCS, BoP. Decide the architecture of those relationships: sole-source vs dual-source, co-development depth, IP boundaries. 

• Set the technical qualification process used by the team and enforce it. Run the highest-stakes design reviews and resolve the highest-stakes vendor escalations personally. 

Engineering Leadership & Mentorship 

• Mentor and develop other engineers on the team. Build their technical judgment, not just their throughput. 

• Run design reviews. Lead post-mortems on field issues and turn them into product changes. 

• Set the cadence and quality bar for ECR/ECN, FMEA, design reviews, and product handoff. 

External & Cross-Functional Representation 

• Represent ON.energy's product engineering externally — customer technical reviews, vendor escalations, industry working groups, certifying bodies, conferences. 

• Partner with the commercial team on the most technically complex pursuits and proposals — proposing architectures, defending positions, structuring technical exhibits in LTSAs and supply agreements. 

• Brief leadership on technical risk and product roadmap decisions. 

Required Qualifications 

• Bachelor's degree in Electrical Engineering, Power Electronics, or a closely related technical field. MS preferred. 

• 10+ years of hands-on engineering experience in BESS, power electronics, UPS, or comparable mission-critical industrial power systems, with a demonstrated record of operating with minimal direction in a senior technical role. 

• Owned multiple product development cycles end-to-end and independently. You've personally designed and integrated a BESS at the system level, from engineering through commissioning and into live operation, not just handed it off at FAT, and the products are still in the field. 

• Architecture-level decision authority on previous BESS equipment. You've made the trade-off calls others built around, not just executed someone else's architecture. 

• Deep, demonstrable skill in detailed component sizing — fuse coordination, busbar sizing, protection device selection, thermal sizing for enclosed cabinets — at the level required to sign off on production designs. 

• Fluency producing and reviewing SLDs, GAs, schematics, and panel layouts; expert with AutoCAD or equivalent E-CAD; comfortable across mechanical drawings. 

• Strong track record running strategic vendor relationships through design, FAT, serial production, and post-deployment escalation. 

• Excellent written and verbal communication — specs, technical positions, design review leadership, board-level briefings. 

• Willing to travel up to 25–30% for FAT inspections, site commissioning, customer engagements, and vendor reviews. 

Preferred 

• Direct experience with data center / UPS / mission-critical power or utility-scale BESS at the architecture level. 

• Active involvement in standards bodies (UL, IEC, NFPA, IEEE working groups, CSA TC committees) or technical conference contributions. 

• Patents, peer-reviewed publications, or other evidence of recognized technical depth in the field. 

• PE license. 

• Familiarity with UL 9540 / 9540A, NFPA 855, IEC 62619, IEEE 1547, NEC Article 706, plus the relevant codes for target markets. 

• Experience standing up or scaling structured PLM, ECR/ECN, and design-review processes. 

• Multi-domain depth — BMS / cell engineering, PCS / power electronics, thermal / mechanical — alongside the EE core. 

 

For US-based roles - What you’ll get:

• Competitive salary + annual performance-based bonus eligibility
• Medical, dental, and vision insurance
• 401(k) with company match
• Paid time off and company holidays 

For Mexico-based roles - What you’ll get:

• Competitive salary + annual performance bonus eligibility
• Christmas Bonus (Aguinaldo): 30 days
• Major medical expenses and life insurance
• Paid time off and holidays (per local policy)

For all roles:

• Professional development and growth opportunities
• Opportunity to grow with a mission-driven team shaping the future of clean energy
• Equal Opportunity: ON.energy is committed to equal employment opportunity and to maintaining a work environment free of harassment, discrimination, or retaliation.
• Benefits vary by role and location and are subject to change.

Agency Notice: ON.energy does not accept unsolicited resumes from staffing agencies, search firms, or third-party recruiters. Resumes submitted without a fully executed Master Services Agreement (MSA) and a written request from an authorized member of our Talent Acquisition team will be considered the property of ON.energy. No placement fees or compensation will be paid for unsolicited candidate submissions.