diff --git a/docs/hardware-plan.md b/docs/hardware-plan.md
index 8af18ad..3fbd3da 100644
--- a/docs/hardware-plan.md
+++ b/docs/hardware-plan.md
@@ -1,8 +1,10 @@
 # Hardware Plan — flexible MIDI router (v1)
 
-Status: draft 2026-08-21. Custom all-in-one PCB, desktop, USB-powered, **bipolar
-±10 V CV** via onboard ±12 V rails, 3.5 mm TRS MIDI, 4× stereo CV, 64×32 OLED +
-tact buttons (no encoder, low profile).
+Status: draft 2026-08-21. Custom all-in-one PCB, **L-shaped with a LiPo
+battery notch** (~70×58 mm bounding box, 2000 mAh target), desktop, USB or
+battery powered, **bipolar ±10 V CV** via onboard ±12 V rails, 3.5 mm TRS MIDI
+(1 in + 3 mirror out), 4× stereo CV, 64×32 OLED + tact buttons (no encoder,
+low profile).
 
 **MCU target:** develop/test on **RP2040** (Pico W dev board — the firmware
 already runs on it), product on **RP2350**. The RM2 radio module is compatible
@@ -218,15 +220,18 @@ Host PCB responsibilities (from the RM2 datasheet):
 ## 10. Build order (hardware)
 
 1. Schematic (this doc is the spec).
-2. RM2 module footprint + antenna keepout.
-3. RP2040 + flash + USB + SWD.
-4. Power (BQ24075 power-path + LiPo, 3.3 V buck-boost, +12 V boost,
+2. Board outline: L-shape, ~70×58 mm bounding box, bottom-left battery
+   notch (50×35 mm for 2000 mAh cell). RM2 antenna keepout at bottom-right
+   corner; USB-C left, CV top, MIDI right (§12).
+3. RM2 module footprint + antenna keepout.
+4. RP2040 + flash + USB + SWD.
+5. Power (BQ24075 power-path + LiPo, 3.3 V buck-boost, +12 V boost,
    −12 V inverter, 4.096 V + 2.048 V refs, MAX17048 fuel gauge).
-5. CV analog (DAC + difference-amp + offset + trim + bidir protection + TRS).
-6. MIDI TRS circuit.
-7. OLED + buttons.
-8. Keypad header (the Pimoroni keypad connects via a header or is integrated).
-9. PCB layout, DRC, review, fab.
+6. CV analog (DAC + difference-amp + offset + trim + bidir protection + TRS).
+7. MIDI TRS circuit.
+8. OLED + buttons.
+9. Keypad header (the Pimoroni keypad connects via a header or is integrated).
+10. PCB layout, DRC, review, fab.
 
 ## 11. Connection table (netlist source of truth)
 
@@ -377,3 +382,62 @@ Keypad header J11 (Pimoroni RGB Keypad):
 U1.GPIO16, GPIO22, GPIO26, GPIO27, GPIO28 ── unassigned (status LEDs / analog in / future)
 ```
 
+## 12. Board outline (L-shape, battery notch)
+
+The LiPo cell is the single largest item, so the PCB is **L-shaped** — the
+55-ish mm connector square with the **bottom-left quadrant notched out** for
+the battery. The two *long* outer edges of the L carry the two jack rows
+(each needs ~52 mm for 4 jacks); USB-C sits on the short left edge, right
+beside the battery — which is where BQ24075, MAX17048 and the cell pigtail
+want to be anyway.
+
+```
+═══════════════════════════════════════════
+║  CV    CV    CV    CV                     ║   top arm  → CV analog
+║  J7    J8    J9    J10   DAC·refs·opa·±12V ║   (DAC8568, REF3040/2040,
+║                                           ║    2× OPA4192, boost+inverter, LC)
+║ USB-C                                     ║
+╚═══╗                                       ║
+    ║                                       ║
+ B  ║       MIDI   MIDI   MIDI   MIDI       ║   right arm → digital + MIDI
+ A  ║       J6     J5     J4     J3          ║   (6N138, UART, RP2040, flash,
+ T  ║       MCU · flash · RM2 ▼ keepout      ║    RM2, SWD, keypad, OLED, btns)
+    ║       SWD · keypad · OLED · SW1-4      ║
+    ╚═══════════════════════════════════════╝
+      ↑ battery notch (bottom-left, off-board cell)
+```
+
+**Sizing (battery drives the notch):**
+
+| Cell        | Pouch size  | Notch      | Bounding box |
+|-------------|-------------|------------|--------------|
+| 1500 mAh    | ~36 × 30 mm | 36 × 30 mm | ~56 × 55 mm  |
+| 2000 mAh (target) | ~50 × 35 mm | 50 × 35 mm | **~70 × 58 mm** |
+
+Both long arms clear the 52 mm the jacks need (top arm = full width, right
+arm = full height). USB-C (~9 mm) fits the short left edge either way.
+Target the **2000 mAh / ~70 × 58 mm** outline; a 1500 mAh cell just shrinks
+the notch.
+
+**Edge assignment:**
+- **Top edge:** 4× CV jacks (J7–J10), full width.
+- **Right edge:** 4× MIDI jacks (J3 in + J4/J5/J6 mirror out), full height.
+- **Left edge (short, top-arm left end):** USB-C (J1).
+- **Bottom edge (short, right-arm bottom end):** SWD header (J2), keypad
+  header (J11), battery pigtail — accessible, non-user-facing.
+
+**Region assignment (the split is functional, not just compact):**
+- **Top arm = all analog/CV + the two switching converters.** Keeps the ±12 V
+  boost/inverter noise up near the CV op-amps and far from the radio/MCU.
+  Inductors + LC against the top edge; DAC8568, REF3040, REF2040, 2× OPA4192
+  follow.
+- **Right arm = digital + MIDI + radio.** RP2040 + flash + RM2 + 6N138 + UART.
+  **RM2 at the bottom-right outer corner** of the right arm — the point
+  farthest from the battery, jacks, and switching converters — with its
+  antenna keepout extending off the corner (best RF spot on an L-board).
+- **Battery + charger (bottom-left notch area):** short USB-C → BQ24075 →
+  cell traces, MAX17048 fuel gauge beside them.
+- **Inner L corner (top-right inside):** quietest spot on the board — put the
+  DAC→op-amp routing and the reference/analog star-ground here, sandwiched
+  between the analog and digital arms but off both edges.
+