Chemistry Leak Versus Load Calculation Audit

Chemistry Leak Versus Load Calculation Audit

Ada treats self-discharge as a parallel current before trusting a cell’s capacity number

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Ada ADA · CALCULATION AUDIT

Chemistry Leak Versus Load Calculation Audit

The chapter compares two chemistries for the same 15 uA sensor and a 10-year target. A 2600 mAh Li-SOCl2 cell leaks only about 3 uA, so it clears the target with margin; a 2000 mAh Li-ion cell leaks about 55 uA — nearly four times the load — and fails at 3.3 years. This audit treats self-discharge as a parallel current to show chemistry leak versus load, and why capacity alone does not decide.

Companion to the chapter Energy-Aware Case Studies — every number here comes from that chapter.

Treat self-discharge as a parallel current before trusting the capacity number. The same 15 uA sensor can pass or fail on chemistry alone.

See the relationship before changing it

The figure reads from left to right. The blue card is cell leakage. The middle card applies the page rule. The green card is ideal life with reserve. Walk the arrows once: set the input, apply the rule, then read the result with its unit.

Cell leakage changes ideal life with reserve An input card leads through the rule life = 2080 mAh / ((15 uA + leakage) / 1000) / 8766 to the ideal life with reserve result. INPUT PAGE INPUT APPLY THE RULE predict calculate check units OUTPUT RESULT
Walk the arrows. Leakage is a parallel current. Capacity matters only after that current joins the load.

Derive the baseline in four named moves

  1. 1

    Name the input. The chapter baseline is 2.966 uA.

  2. 2

    Name the relationship. life = 2080 mAh / ((15 uA + leakage) / 1000) / 8766

  3. 3

    Substitute with units. 2080 / ((15 + 2.966) / 1000) / 8766 = 13.21 years

  4. 4

    Read the result. Keep the unit beside the value. Use it only inside the technical boundary on this page.

Predict, then change cell leakage

Try Predict the direction of life = 2080 mAh / ((15 uA + leakage) / 1000) / 8766. Test another cell leakage, then compare ideal life with reserve.

2.966 uA
Chapter baseline
Ideal life with reserve

Observe Leakage is a parallel current. Capacity matters only after that current joins the load. Reset cell leakage to 2.966 and compare ideal life with reserve.

Explain Leakage is a parallel current. Capacity matters only after that current joins the load.

Check yourself

What should you do before trusting a moved-control result?
Answer: Predict its direction, apply the shown relationship, keep the units, and reset to the worked baseline.
What does this small model leave out?
Answer: Only cell leakage moves here. Field effects named in the technical boundary stay fixed.

Honesty note. This teaching model changes only cell leakage. It is not a field prediction.

TryChemistry Leak Versus Load” from the shown inputs: The chapter compares two chemistries for the same 15 uA sensor and a 10-year target. Use Check derivation.
ObserveThe displayed ledger resolves 15 uA, 10-year, 2600 mAh, 3 uA, 2000 mAh at full precision. This audit treats self-discharge as a parallel current to show chemistry leak versus load, and why capacity alone does not decide. Check derivation shows this.
ExplainThe physics check is the result: capacity is only useful after the chemistry leak is subtracted from the lifetime budget. The Li-SOCl2 case survives the 10-year target with reserve; the Li-ion case fails before temperature and ageing penalties are even added. Check derivation confirms it.

Chemistry leak versus load

  • Li-SOCl2 leak: 2600 mAh x 0.01 = 26 mAh/year; 26 mAh / 8766 h = 0.002966 mA = 2.97 uA.
  • Li-SOCl2 operating draw: 15 uA + 2.97 uA = 17.97 uA, rounded in the prose to about 18 uA.
  • Usable capacity with 20% reserve: 2600 mAh x 0.80 = 2080 mAh; lifetime 2080 mAh / 0.017966 mA = 115774 h; 115774 h / 8766 h/year = 13.21 years.
  • Li-ion leak: 2000 mAh x 0.02 = 40 mAh/month; 40 mAh / 730 h = 0.0548 mA = 54.8 uA.
  • Li-ion total draw: 15 uA + 54.8 uA = 69.8 uA; even with 2000 mAh usable, 2000 / 0.0698 = 28653 h = 3.27 years.

The physics check is the result: capacity is only useful after the chemistry leak is subtracted from the lifetime budget. The Li-SOCl2 case survives the 10-year target with reserve; the Li-ion case fails before temperature and ageing penalties are even added.

Technical boundaries
The chemistry ledger deliberately does not simulate pulse voltage sag, temperature, capacity fade, passivation, cutoff voltage, load variation, or calendar-aging curves; it converts the chapter's average leakage rates into parallel current.

Work the audit first, then check the displayed derivation.

Every number above is taken from this chapter's own worked example and re-derived step by step.