What watt-hours, voltage, and C-rating actually mean when you're buying a robot battery.
A battery's headline numbers tell you three things: how much energy it holds, how hard it can push, and how long it lasts. Energy is measured in watt-hours (Wh) — voltage multiplied by amp-hours. A 46.8 V, 9 Ah pack holds about 421 Wh. Runtime follows energy divided by average power draw, which is why the same pack lasts two hours in a lab demo and half that in heavy manipulation.
Voltage sets the system's operating point — motors and drivers are designed around it, which is why you can't substitute a 28 V pack where a 48 V one belongs. The C-rating describes discharge capability: a 1C rating means the pack can deliver its full capacity in one hour; humanoid joints demand high burst current during dynamic moves, so peak C-rating matters more than the headline capacity for performance.
Cycle life — typically 500 to 1,000 full cycles for lithium-ion — determines replacement timing. Depth of discharge, charge voltage, and temperature all move that number. The practical takeaway: buy the OEM pack, store at partial charge, and replace when runtime drops ~30% from spec.
Watt-hours combine voltage and capacity into one energy number, so you can compare packs across voltages. Two packs at 9,000 mAh aren't equivalent if one is 28 V and the other is 48 V — the 48 V pack holds far more energy.
It depends on the joint torque demands, but dynamic bipeds pull high burst currents. This is exactly why underspecified third-party packs are dangerous — they sag or overheat under peak load. OEM packs are rated for the robot's actual duty cycle.
Only if voltage matches and the robot can carry the weight. Oversized packs add mass that the joints must move, which eats into the gains. Stick with the manufacturer's spec.