What is battery-aware design, and how does Peukert's law change how you evaluate a low-power architecture?

Short Answer

Battery-aware design judges a chip by the shape of its current draw, not just its average power. Peukert's law says a battery delivers less total charge when drained at a higher current, so a bursty design can run out sooner than a smooth one with the same average.

Technical Explanation

• Peukert's law: effective capacity falls as discharge current rises. The exponent k captures how strongly.
• k is near 1 for lithium-ion cells and larger for lead-acid, so the effect size depends on chemistry.
• High peaks also cause internal-resistance voltage droop, which can trip a brownout reset even when charge remains.
• So peak-to-average ratio matters: spread work out, stagger domain wake-ups, and avoid all blocks bursting at once.
• Duty-cycled designs with short, high bursts gain the most from smoothing.
• Recovery effect: a cell regains some usable charge while it rests, so Peukert on a pulsed load gives an estimate, not an exact answer.
• An average-power spreadsheet alone can overstate real battery life.

Formula Or Decision Rule

• Peukert's law: t = C_p / I^k
• C_p = capacity at 1 A discharge, I = discharge current, k = Peukert exponent (1.0 is ideal)
• Rule: at equal average current, the profile with higher peaks drains more capacity when k > 1.

Follow-up Question & Model Response

"How would you reduce peak current in a chip design?"

Candidate Model Response: Stagger the wake-up of power domains so their in-rush and activity bursts do not overlap. Spread compute over a longer window at lower frequency, which DVFS supports. Add local decoupling so short spikes come from on-chip charge rather than the battery. Then measure peak and average current together on the real activity profile. Take the Peukert exponent from the cell data sheet or fit it from discharge curves at two currents.