# R3.6 battery subsystem

## Design basis and fit

The supplied original R3.4 is the geometry baseline. The final native exterior comparison retains the original nominal surfaces and dimensions; the rigid case remains 78 × 150 × 24 mm. No R3.5 enlarged shell geometry was used.

The owner selected Adafruit 2011. The [product page](https://www.adafruit.com/product/2011) lists 60 × 36 × 7 mm nominal. Its [linked supplier drawing](https://cdn-shop.adafruit.com/datasheets/LiIon2000mAh37V.pdf), page 5, gives 62 × 38.5 × 8.5 mm maximum. The latter is the design envelope, separate from added assembly clearance. It does not verify the received taped tab or establish a swelling allowance.

The maximum body occupies X −31…31, Y 27.28…65.78 and Z −16.60…−8.10 mm. The nominal reference is rotated 180° in its plane so the protected tab is on the right. The bare rigid cavity is 62.6 × 39.1 mm, with 0.30 mm clearance at each side and end. The rigid clearance extends 0.15 mm behind and 0.25 mm in front of the maximum body.

Original tall rails and posts are replaced by a low cradle and two removable keeper plates. A broad toe on each keeper sits in front of the PCB, so a thin fence is not squeezed between the pouch and board. The original front shell needs matched internal keeper, head and toe reliefs. Both keepers have outward-open wiring ports.

## Hardware and stock

Four M2 × 6 pan-head screws secure the keepers to rigid stops. The model reserves a head envelope of Ø4 × 1.6 mm; verify the purchased screws. Their head seats are Z −5.8 and the post tops are Z −8.4. Nominal engagement is 3.4 mm, with 1.2 mm tip-to-pilot-floor margin. Through holes are Ø2.4, pilots Ø1.7 and post diameter Ø4.6. The clipped inboard post wall remains 1.25 mm from the pilot. Use process coupons before choosing the actual pilot diameter.

All soft-stock dimensions below are **installed dimensions including adhesive**. Use nonabrasive, electrically insulating purchased stock. These are not rigid printed parts.

| Stock | Quantity | Dimensions, mm | Placement |
|---|---:|---|---|
| Rear support pads | 2 | 14.5 × 27.5 × 0.70, R1 corners | Centres X ±21.25, Y46.5; Z −17.3…−16.6 |
| Default keeper contact films | 4 | 7.5 × 3 × 0.10, R0.6 corners | Left centres (−26.25,44.4)/(−26.25,50.9); right (26.25,37.5)/(26.25,51.65); Z −7.9…−7.8 |
| Lower toe liners | 2 | 8.7 × 0.20 × 2.2 | X −30.7…−22 and 22…30.7; Y26.98…27.18; Z−10.1…−7.9 |
| Optional nominal-only keeper pads | 4 | 7.5 × 3 × 1.40 | Replace the default films at the same locations; never stack |

The default films leave 0.20 mm of front clearance for an 8.5 mm thick pack. The optional 1.40 mm pads are permitted only where the measured local gap before the pad is at least 1.60 mm. They leave 0.40 mm with the nominal 7 mm body and must not be fitted with the maximum gauge.

The toe liners leave 0.10 mm of downward travel for the maximum pack. At that limit, the nominal PCB-edge gap is only **0.22 mm**. This is a tight qualification gate, not a guaranteed clearance. Hold release if the actual board, pouch, print and pad stack permits rubbing, pinching or a nonpositive gap. Pouch rocking and liner compression must also be checked physically.

## Assembly and removal

1. Print and measure the inert maximum gauge and the footprint coupon in the intended process. Reject a forced fit. Check pilot and keeper/root coupons before the complete assembly.
2. Keep the front shell and both battery keepers removed. Fit the rear support pads and lower the inert gauge straight into the cradle. The CAD checks cover this straight Z path and the original nominal body/tab reference.
3. Confirm a real maximum-sized gauge can be installed and lifted out without contacting the PCB edge. Do not use a live pouch as an interference gauge.
4. Select soft stock from measured gaps. Install the keepers on their rigid stops; they must not preload the pouch. Check the full allowed motion and the gap to the PCB.
5. Use the final inward risers for the intact factory lead and plug. The older outward route is excluded. The paired nominal 100 mm routes leave 0.20 mm wire-to-wire clearance and approximately 1.0 mm minimum channel-to-exterior material; qualify actual lead length, dressing and print tolerance. Preserve all protected tab material, tape and protection circuitry. The old 100 mm CAD lead placeholders do not establish available wire length. The compact removable adapter and its polarity remain separate verification items.
6. To service the battery, open the case, free the documented removable connection and lead dressing, remove both keepers, then lift along Z while keeping the lower pouch edge away from the board. Do not drag the pouch across the PCB edge.

## CAD and structural evidence

- Use the matched native STEP/STL files in Print_Parts. Final battery keepers and both shell exports are valid single solids with watertight, consistently wound single-component print meshes; final verification is indexed in Verification/integrated/FINAL_VERIFICATION.json.
- The bounded, axis-aligned maximum-body translation sweep has nominal gaps of 0.22 mm to the PCB, 0.25 mm to the speaker body, 0.30 mm to P18, 0.75 mm to the revised upper speaker screw heads, and 0.85 mm to nominal Ø2.5 closure shafts. These do not simulate flexible-pouch deformation, rocking or print error.
- The front-shell keeper-head relief leaves 1.0983 mm. A separate final battery-wire channel leaves approximately 1.0 mm to the original curved exterior. The rear upper corner reaches 0.9529 mm in a small supported curved region. The wall map includes exact BRep minimum distances and approximate thin-region areas/spans. These local skins need process and handling qualification; a scalar minimum is not a strength test.
- The keeper has a 3 mm main plate, a 2.6 mm supported outboard neck/seat and a short 2 mm inboard transition. Under the root's hypothetical E = 1000 MPa and allowable = 8 MPa, separate conservative 5 N section screens give approximately 6.90, 7.42 and 6.74 MPa. These are simplified gross-section calculations, not validated material properties or a full contact analysis.
- Assuming a 40 g pack, 10 N total keeper load corresponds to about 25.5 g of static inertia. No drop test is implied. Weigh the actual pack.

Physical gates remain: coupon fit and 5 N keeper/root screening, ten assembly/service cycles, retention and rocking checks, and verification of the final wire route. No physical certification is claimed.

See [battery provenance and dimensions](../Verification/battery/FINAL_INTEGRATION_MANIFEST.json), the [final riser treatment](../Verification/fixtures/BATTERY_RISER_FINAL_MANIFEST.json), and the complete [assembly instructions](Assembly_and_Qualification.md). The final integrated print files take precedence over intermediate subsystem trials.


## Final screw-driver sequence

The final 77d9a0a5 assembly audit checks all 32 nominal screw axes with a straight Ø3 × 30 mm shaft. See [Driver_Access_and_Fastening_Order.md](Driver_Access_and_Fastening_Order.md). Keep F01 off during internal work and closure tightening. The front subassembly/PCB remains separate during rear antenna and battery work. Fit the antenna before the battery, because the maximum battery covers the two upper antenna tool paths.

Fasten the battery keepers before finally dressing factory lead 2 through the inward riser. The right lower screw (screw 3, X33.4, Y37.5) has a 1.1174 mm³ tool overlap with that lead in its final dressed route. Keep the intact lead free outside the driver corridor during fastening; preserve its tab/protection, avoid tension and tight folds, then dress it to the checked final path. Release that local dressing before service. Do not use a driver to push the lead aside. Battery screw 1 is also close to the final J10 pigtail-2 route (0.1317 mm); keep the front harness separate/undressed while performing this rear work.

Likewise, fasten the volume captures before dressing J9 common link 1. Tighten all four case-closure screws with F01 off, then fit the flexible bumper. For service, remove the bumper first; remove the battery before upper antenna screw access. These are nominal CAD shaft checks. Actual tool fit, wire handling, tolerance and ten assembly/service cycles remain physical qualification requirements.