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Battery Systems & Power Architecture

Duration: 45 min · Level: Intermediate · Module: 2. Actuator Architecture · Focus: battery, power, energy, systems

Learning objectives

By the end of this lesson you will be able to explain and apply:

  • Power budget estimate
  • Lithium-ion 21700 cells
  • Tesla Optimus uses lithium iron phosphate (LFP) cells for…
  • Power delivery
  • Regenerative braking

Why this matters​

G1 targets 8+ hours of operation — this is the spec that enables a full hospital shift or home-care day without charging.

Overview​

G1 targets 8+ hours of operation — this is the spec that enables a full hospital shift or home-care day without charging. Achieving this requires careful energy budgeting, high-density battery selection, efficient power delivery architecture, and regenerative braking on large joints.

Key concepts​

Key idea

Power budget estimate: 40-joint humanoid at moderate activity draws 800W-1.5kW average; 8 hours → 6.4-12 kWh capacity needed

  • Lithium-ion 21700 cells: ~270 Wh/kg energy density; 12 kWh pack weighs ~44kg — too heavy; target 6 kWh with duty-cycle optimization
  • Tesla Optimus uses lithium iron phosphate (LFP) cells for safety; slightly lower energy density but safer in impact scenarios
  • Power delivery: 48V bus architecture standard for humanoids; reduces cable weight and I²R losses vs 24V; modern GaN inverters achieve 98%+ efficiency
  • Regenerative braking: knee flexion and ankle dorsiflexion during stair descent can recover 15-25% of locomotion energy
  • Hot-swap battery design: allow battery change in <2 minutes; two 3 kWh packs in parallel, one removable while robot remains operational

Check your understanding​

Try to recall each answer before expanding it.

Q1. What do you know about Power budget estimate?

40-joint humanoid at moderate activity draws 800W-1.5kW average; 8 hours → 6.4-12 kWh capacity needed

Q2. What do you know about Lithium-ion 21700 cells?

~270 Wh/kg energy density; 12 kWh pack weighs ~44kg — too heavy; target 6 kWh with duty-cycle optimization

Q3. What do you know about Tesla Optimus uses lithium iron phosphate (LFP) cells for…?

Tesla Optimus uses lithium iron phosphate (LFP) cells for safety; slightly lower energy density but safer in impact scenarios

Q4. What do you know about Power delivery?

48V bus architecture standard for humanoids; reduces cable weight and I²R losses vs 24V; modern GaN inverters achieve 98%+ efficiency

Q5. What do you know about Regenerative braking?

knee flexion and ankle dorsiflexion during stair descent can recover 15-25% of locomotion energy

← Previous: 2.3 Joint-Level Architecture for a Full Humanoid · Next: 2.5 Thermal Management & Actuator Reliability →

Part of Module 2: Actuator Architecture.