20260922-2048-air-cr2450-battery-baseline Move the Air battery baseline to a single CR2450 and re-select the first-version platform

status: completed
createdAt: 2026-09-22 20:48
approvedAt: 2026-09-23 11:24
relatedTask: 20260922-2048-air-cr2450-battery-baseline

Context

The owner's instruction is one line, "电池考虑 CR2450", written after the evaluation bizplan/product/switch/air/evaluations/ti-cc2340-touch-battery.md showed that every candidate SoC except the ESP32-H2 runs from 1.7–1.9 V with ≤11 mA radio peaks, so a CR2450 can feed the SoC directly. Two readings exist: (1) rank CR2450 first in the evaluation only; (2) make CR2450 the Level 1 battery baseline again. Reading (1) is a two-line edit of a non-binding page and changes nothing downstream; reading (2) is the decision this plan describes. The proposal below is written for reading (2) and the owner can drop to (1) with one word.

What the CR2450 decision drags along

Platform. The 2026-09-11 decision adopted the ESP32-H2 because 2×AAA plus a buck-boost removed its three coin-cell blockers (3.0 V floor, 0.35 A peak, 7 µA sleep). On a CR2450 the H2 is out again; the first-version recommendation must move to a part with a ≤2.0 V floor and ≤11 mA peaks. From the evaluation the candidates are nRF54L15 (0.6 µA, 3.2/5.0 mA, NFC, already the documented backup), TI CC2755R10 (0.9 µA, 6.1/7.7 mA, HSM, Matter, no NFC) and TI CC2674R10 (if touch input is ever wanted). CC2340R5 stays out until TI confirms secure boot / debug lock.
Budget. Energizer CR2450: 620 mAh at 7.5 kΩ to 2.0 V. With the same 65 % derating the spec uses for AAA, the comparison budget is 400 mAh, the figure the H2 evaluation §4.3 used before 2026-09-11: 2 years 22.83 µA, 3 years 15.22 µA, 5 years 9.13 µA, 10 years 4.57 µA. The evaluation's order-of-magnitude estimate for nRF54L15 or CC2755R10 fed directly is 9–14 mAh a year, so the three-year target has margin and the five-year target is plausible, subject to measurement.
Peak current on an ageing cell. The CR2450 datasheet's pulse curve shows internal resistance climbing from tens of ohms to about 100 Ω near end of life. A 5 mA radio event across 100 Ω drops 0.5 V; from a 2.4 V open-circuit voltage that lands at 1.9 V, above the 1.7 V floor but with no margin for an +8 dBm burst. The design therefore needs a low-leakage ceramic storage capacitor (C ≥ I × Δt / ΔV: 5 mA × 2 ms / 0.1 V = 100 µF order) and a TX-power cap at low battery, plus the 10 µF input capacitor the CC2340 datasheet asks for on coin cells. This is a fifth of the 1250 µF the H2 evaluation estimated for the H2, and ceramics at this value leak far less than the tantalum the H2 case implied.
Thickness. CR2450 is 5.0 mm thick; the ≤12 mm target that was relaxed to ≤14 mm on 2026-09-11 for the AAA compartment can be restored.
Compliance. Coin cells add child-resistant battery-compartment requirements (US 16 CFR 1263 "Reese's Law", IEC 62368-1 / IEC 60086-4 guidance; the Energizer datasheet itself asks for a tool or two simultaneous movements to open) and lithium-metal transport documents (UN 3090/3091), which replace the AAA cylindrical-cell line under AIR-O-06.
Low-battery threshold. AIR-05 keeps its 2.4 V initial threshold, but the value must be read under load and the hysteresis calibrated against the rising internal resistance; the 2.0 V datasheet cutoff is the floor for capacity, not for the threshold.

Pages that carry the AAA baseline today

File	Lines / fields	Change
`bizplan/product/switch/air/P05-air.md` (spec R0.4)	§2 电池, 外形目标, 电池维护; §3 AIR-01; §7; §8 AIR-O-05, AIR-O-06; §9	battery, thickness, budget, requirement text, compliance items, change log R0.5
`bizplan/product/switch/air/P05-air-design.md` (R0.1)	§2.1 table, §2.2 table and prose, §3 diagram, §4 budget table and electrical requirements, §7, §8	platform recommendation, diagram, 400 mAh table, coin-cell electrical rules, change log R0.2
`bizplan/product/switch/air/evaluations/esp32h2.md`	§1 dated note	add a 2026-09-22 note: the AAA decision is superseded; H2 no longer first-version
`bizplan/product/switch/air/P05-air-brief.md`	lines 26, 40	battery and thickness wording
`bizplan/product/switch/air/index.md`	intro line, design row content	battery and platform wording
`bizplan/product/switch/P05-switch.md`	Air row	battery cell
`bizplan/product/switch/P05-switch-brief.md`	Air bullet	battery wording
`bizplan/product/switch/air/P05-air-guide.md` (R0.1)	V-08 row, §7 quotation line	child-resistant compartment test; coin-cell transport wording; change log
`bizplan/governance/product-plan.md` §P5	型号, 外形/环境目标, 无线推荐, 维护目标 rows	battery, thickness, platform, 400 mAh / 15.22 / 9.13 µA
`bizplan/governance/open-questions.md`	items 3 and 4	platform and battery wording

The 2026-09-22 evaluation page is left as written; it is the evidence the decision cites.

Proposal

Adopt the single CR2450 as the Air battery baseline and make the platform change it forces.

A. Spec `P05-air.md` → R0.5

§2 电池: "1×可更换 CR2450 一次锂纽扣电池（Li-MnO2，IEC CR2450），不充电；SoC 由电池直接供电，不设升压或 buck-boost".
§2 外形目标: "总厚度 ≤12 mm（2026-09-22 由 ≤14 mm 恢复；2026-09-11 的放宽随 AAA 方案一起撤销）".
§2 电池维护: "整机可用容量暂按 400 mAh 作预算（620 mAh 标称 × 65 %），三年目标对应平均负载 ≤15.22 µA、五年 ≤9.13 µA".
§3 AIR-01: "…1×CR2450 一次锂纽扣电池、用户可更换，无充电路径；电池仓须满足儿童防护要求（工具开启或两个同时动作）".
§7: replace the cylindrical-cell transport sentence with coin-cell transport (UN 3090/3091) and the child-resistant compartment regulations under AIR-O-06.
§8 AIR-O-05: "含 CR2450 电池座的结构堆叠与 ≤12 mm 验证、儿童防护电池盖…"; AIR-O-06 gains "纽扣电池儿童防护法规（16 CFR 1263、IEC 62368-1）".
§9: R0.5 row citing this task.

B. Design appendix `P05-air-design.md` → R0.2

§2.1: first-version recommendation nRF54L15 (QFN), reasons: 1.7 V floor, 3.2/5.0 mA, 0.6 µA, NFC-A keeps the authenticated OOB path of AIR-O-02; TI CC2755R10 as the documented alternative (HSM, Zigbee 3.0 / Matter certified, no NFC); CC2674R10 noted only for a touch variant. Battery row: "CR2450 直供 + 10 µF 输入电容 + 低漏电陶瓷储能电容（初算 100 µF 量级）".
§2.2: table becomes A nRF54L15 / B CC2755R10 / C ESP32-H2 (rejected: coin cell) / D ESP32-C6 (rejected), with the "为什么" prose rewritten: the H2 reasoning of 2026-09-11 rested on the AAA pack.
§3 diagram: CR2450 -- reverse/short protection -- 10 µF + storage cap -- SoC.
§4: budget table for 400 mAh; formula Iavg = 400000 / (365 × 24 × 年数); electrical requirements rewritten for 3.0 → 2.0 V, verification points 3.0 / 2.4 / 2.0 V, storage-capacitor sizing with end-of-life IR (about 100 Ω) and a TX-power cap at low battery, low-battery measurement under load.
§7: child-resistant battery door and coin-cell holder retention in the structure list.
§8: R0.2 row.

C. Other pages

evaluations/esp32h2.md §1: one dated paragraph that the 2026-09-11 AAA decision is superseded on 2026-09-22 by the CR2450 decision and that the H2 is no longer the first-version recommendation; the rest of the page stands as record.
Brief, line spec, line brief, package index: battery and thickness wording, one line each.
Guide V-08: add child-resistant compartment opening test; §7: coin-cell transport wording; change log R0.2.
product-plan.md §P5: four rows; open-questions.md: items 3 and 4.
docs/changelog.md: one decision entry.

Verification: bun run docs:lint && bun run docs:build && git diff --check; grep that no page outside change logs still states 2×AAA, ≤14 mm or 750 mAh for Air; every AIR-nn and AIR-O-nn ID present before is present after.

Risks

Platform change is the real decision. CR2450 cannot be adopted while the ESP32-H2 stays the first-version part. The proposal picks nRF54L15 first and CC2755R10 as the alternative; the owner may prefer the TI part first, which changes §B only.
End-of-life pulse margin. The 100 Ω figure is read from the Energizer pulse chart; the storage capacitor and the low-battery threshold need bench data (AIR-O-07) before the five-year target can be claimed.
Cold cabin. CR2450 is rated −30 °C, inside the −20 °C target, but capacity and IR at −20 °C are not on the datasheet; a −20 °C measurement joins V-04.
User replacement. Coin cells are less likely to be substituted by a wrong chemistry than AAA, but CR2450 vs CR2477 confusion (7.7 mm thick) must be blocked mechanically or accepted.
Regulation. Child-resistant compartment rules add a test and possibly a tool-opened door, which touches the installer experience in the brief.
The 2026-09-11 decision is reversed within eleven days; the change logs must say why (the SoC supply floor moved, not the battery data).

Scope

Edit: 10 files listed above (spec, design, guide, brief, package index, H2 evaluation, line spec, line brief, product plan, open questions).
Tracking: this plan, task 20260922-2048, changelog.
Not in scope: the Air Hub, Mate, Key pages; the sub-GHz open item AIR-O-09; touch input (AIR-O-10 is not opened by this plan).

Alternatives

Reading (1): evaluation-only. Change the evaluation's §5 item 4 to rank CR2450 first and stop. No Level 1 change, no platform change; the AAA + H2 baseline stays until D0. Cheapest, but leaves the spec recommending a part and a battery the owner has just moved away from.
CR2450 with ESP32-H2 kept via boost converter. Rejected: the H2 evaluation §4 showed the boost, the 1250 µF storage and the 7 µA sleep leave no engineering margin on a coin cell.
CR2477 instead of CR2450. About 1000 mAh but 7.7 mm thick, which forfeits the ≤12 mm target; not proposed, can be a listed alternative in AIR-O-05.
TI CC2755R10 first, nRF54L15 alternative. Same edits, swapped; loses the NFC OOB path and keeps AIR-O-02 open exactly as with the H2.

Annotations

2026-09-22 (owner): "电池考虑 CR2450". Plan written for the baseline-change reading.
2026-09-23 11:24 (owner): "开始" — approved; no platform preference stated, so the proposal's default (nRF54L15 first, CC2755R10 alternative) is implemented.