Principal Battery Systems Engineer

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…