Reconciling “8 Years” With “20-40 mAh/day”

Reconciling “8 Years” With “20-40 mAh/day”

Ada re-derives this chapter’s own numbers step by step, at full precision

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Ada ADA · CALCULATION AUDIT

Reconciling "8 Years" With "20-40 mAh/day"

The chapter carries two polling-energy figures that look contradictory: the headline says HTTP polling costs 20 to 40 mAh/day, while a connection-overhead panel derives about 8 years of battery — barely 1 mAh/day. Both are the chapter’s own numbers for 144 connections a day. This audit reconciles “8 years” with “20-40 mAh/day” by finding the one hidden variable: active radio time per poll.

Companion to the chapter HTTP Connection Pitfalls — every number here comes from that chapter.

See the relationship before changing it

The figure reads from left to right. The blue card is radio awake time. The middle card applies the page rule. The green card is daily charge. Walk the arrows once: set the input, apply the rule, then read the result with its unit.

Radio awake time changes daily charge An input card leads through the rule charge = 100 mA x awake seconds / 3600 x 144 polls/day to the daily charge result. INPUT PAGE INPUT APPLY THE RULE predict calculate check units OUTPUT RESULT
Walk the arrows. Seconds awake per poll can move the battery result far more than handshake byte count.

Derive the baseline in four named moves

  1. 1

    Name the input. The chapter baseline is 5 s/poll.

  2. 2

    Name the relationship. charge = 100 mA x awake seconds / 3600 x 144 polls/day

  3. 3

    Substitute with units. 100 x 5 / 3600 x 144 = 20.00 mAh/day

  4. 4

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

Predict, then change radio awake time

Try Predict the direction of charge = 100 mA x awake seconds / 3600 x 144 polls/day. Test another radio awake time, then compare daily charge.

5 s/poll
Chapter baseline
Daily charge

Observe Seconds awake per poll can move the battery result far more than handshake byte count. Reset radio awake time to 5 and compare daily charge.

Explain Seconds awake per poll can move the battery result far more than handshake byte count.

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 radio awake time moves here. Field effects named in the technical boundary stay fixed.

Honesty note. This teaching model changes only radio awake time. It is not a field prediction.

TryThe ledger assumes 144 polls/day and contrasts short versus extended radio-on time; it does not simulate DNS, TCP/TLS handshakes, retransmissions, keep-alive reuse, tail energy, or battery ageing.
ObserveThe lifetime result moves from roughly 8 years toward the 20-40 mAh/day headline when active time per poll is expanded.
ExplainDaily charge is current multiplied by radio-on duration and poll count; the hidden per-poll duration therefore reconciles the apparently conflicting lifetimes.

Ada: This chapter carries two polling-energy numbers that look contradictory — the headline says HTTP polling costs 20 to 40 mAh/day, while the connection-overhead panel derives a battery life of about 8 years, which is barely 1 mAh/day. Both are the chapter’s own figures, so let me show they describe the same device at two levels of fidelity.

  • Polling every 10 minutes gives 86400 / 600 = 144 connections/day — the shared anchor for both numbers.
  • The idealized handshake model uses E = 80 mA x 270 ms + 20 mA x 180 ms = 21.6 + 3.6 = 25.2 mA·s per connection (its stated ~450 ms of active radio), i.e. 25.2 / 3600 = 0.007 mAh. Daily: 0.007 x 144 = 1.008 mAh/day, so 3000 / 1.008 = 2976 days ≈ 8.15 years. That reproduces the panel exactly.
  • But the pitfall text itself states each poll holds the radio awake 3 to 5 s at 50 to 100 mA. Taking 5 s x 100 mA = 500 mA·s = 0.1389 mAh per connection: 0.1389 x 144 = 20 mAh/day — exactly the headline’s lower bound.
  • The two models differ by 500 / 25.2 = 19.8x, which is precisely why 8.15 years collapses to 3000 / 20 = 150 days once real radio wake time is counted.

The audit conclusion is that neither number is wrong; the one hidden variable is active radio time per poll, and it swings the battery estimate nearly twenty-fold — so the figure you must actually measure on the device is seconds-awake-per-wake, not handshake byte count.

Technical boundaries
Fixed per-poll radio time brackets this comparison; retries, variable server latency, payload processing, tail states, conversion loss, and cell ageing are omitted.

Work the audit first, then check the displayed derivation.

Every number above is taken from the chapter’s own material and re-derived step by step.