diff --git a/README.md b/README.md
index 257f4bd..fa5b96f 100644
--- a/README.md
+++ b/README.md
@@ -13,8 +13,10 @@ A cyberdeck built from salvaged ASUS K501U laptop components and Orange Pi 5 SBC
 - [x] USB expansion design
 - [x] Case nomenclature and orientation defined
 - [x] Build approach: wooden case + salvaged lid canopy
+- [x] Input device: ThinkPad TrackPoint keyboard
+- [x] Power system: IP5389 board + 18650 cells (preliminary)
 - [ ] Case design (dimensions, internal layout)
-- [ ] Power system (battery, charging)
+- [ ] Power system board selection and testing
 - [ ] Bow wall design (power input, fan exhaust)
 - [ ] Fabrication
 - [ ] Software configuration
@@ -54,6 +56,7 @@ A cyberdeck built from salvaged ASUS K501U laptop components and Orange Pi 5 SBC
 - [USB Expansion](docs/usb-expansion.md) - Hub selection and port allocation
 - [Parts List](docs/parts-list.md) - Bill of materials with costs
 - [Design Decisions](docs/design-decisions.md) - Build approach, nomenclature, layout
+- [Power System](docs/power-system.md) - IP5389 battery management decision
 
 ## Quick Reference
 
@@ -69,7 +72,7 @@ A cyberdeck built from salvaged ASUS K501U laptop components and Orange Pi 5 SBC
 - **Board:** Orange Pi 5 (RK3588S, base model, 16GB RAM)
 - **Storage:** MicroSD slot + USB 3.0 external
 - **USB:** 1× USB 3.0, 2× USB 2.0 native
-- **Power:** 12V 2A barrel or USB-C PD
+- **Power:** USB-C PD via IP5389 power board, 18650 cells
 
 ### Cost Estimate
 
@@ -77,8 +80,8 @@ A cyberdeck built from salvaged ASUS K501U laptop components and Orange Pi 5 SBC
 |----------|------|
 | SBC | ~$104 |
 | Display controller | ~$24 |
-| Storage (SD + hub + enclosure) | ~$35-50 |
-| Power supply | ~$10 |
-| **Subtotal** | **$170-190** |
+| Storage (SD + hub + enclosure) | ~$32-44 |
+| Power system (board + cells + fuse + charger) | ~$32-56 |
+| **Subtotal** | **$206-230** |
 
-(Excludes case materials, battery, misc hardware)
\ No newline at end of file
+(Excludes case materials and misc hardware. Battery included in power system.)
\ No newline at end of file
diff --git a/docs/design-decisions.md b/docs/design-decisions.md
index 6d480d3..4cbf9b7 100644
--- a/docs/design-decisions.md
+++ b/docs/design-decisions.md
@@ -36,6 +36,14 @@ User sits at the **stern**, facing the **bow**. Hinge axis runs port-to-starboar
 
 ### Bow Wall Functions
 
-- Power input (barrel jack or USB-C PD)
+- Power input (USB-C for IP5389 board charging)
 - Exhaust fans blowing away from user
 - Heat management surface
+
+## Power System
+
+IP5389 power bank board (preliminary). All-in-one: charging, BMS, USB-C PD output. See [power-system.md](power-system.md) for details.
+
+## Input Device
+
+ThinkPad TrackPoint keyboard (specific model TBD based on availability). Chosen for built-in TrackPoint pointer and 15.6" deck space compatibility.
diff --git a/docs/parts-list.md b/docs/parts-list.md
index bdd9792..abb55d3 100644
--- a/docs/parts-list.md
+++ b/docs/parts-list.md
@@ -32,8 +32,10 @@
 
 | Item | Specification | Source | Est. Cost | Status |
 |------|--------------|--------|-----------|--------|
-| Power supply | USB-C PD or 12V 2A | Amazon | $8-12 | To purchase |
-| (Future) Battery | 10,000-20,000 mAh PD | TBD | $20-40 | Future |
+| IP5389 power board | USB-C PD, 3S, bare PCB | AliExpress | $8-15 | Preliminary selection |
+| 18650 cells | 3S or 3S2P, quality brand | User's pick | $12-24 | To purchase |
+| 5A blade fuse + holder | Automotive | Amazon | $2 | To purchase |
+| USB-C wall charger | 45W+ PD, for charging | Amazon | $10-15 | To purchase |
 
 ### Networking
 
@@ -62,24 +64,24 @@
 | MicroSD | $12 |
 | USB hub | $20 |
 | USB enclosure | $12 |
-| Power supply | $10 |
+| Power system (board+cells+fuse+charger) | $32-56 |
 | WiFi dongle | $12 |
-| **Subtotal** | **$194** |
+| **Subtotal** | **$206-230** |
 
 ### With Optional Items
 
 | Category | Cost |
 |----------|------|
-| Base build | $194 |
+| Base build | $206-230 |
 | Heatsink/cooling | $10 |
 | Panel-mount cables | $15 |
-| **Total** | **$219** |
+| **Total** | **$231-255** |
 
 ### Future Additions
 
 | Category | Cost |
 |----------|------|
-| Battery pack (portable) | $20-40 |
+| Battery pack (portable) | Integrated in base build |
 | Case materials | TBD |
 | Custom PCB | TBD |
 
@@ -96,7 +98,9 @@
 - MicroSD card
 - Powered USB hub
 - USB enclosure or flash drive
-- Power supply
+- IP5389 power board + 18650 cells
+- 5A fuse + holder
+- USB-C PD wall charger (45W+)
 - WiFi dongle
 
 ---
diff --git a/docs/power-system.md b/docs/power-system.md
new file mode 100644
index 0000000..9710a4f
--- /dev/null
+++ b/docs/power-system.md
@@ -0,0 +1,79 @@
+# Power System
+
+## Decision: IP5389 Power Bank Board (Preliminary)
+
+All-in-one power management PCB. Replaces separate charger module, BMS, and boost/buck converter with a single board.
+
+## Why This Approach
+
+| Requirement | IP5389 Solution |
+|------------|-----------------|
+| Charge lithium cells safely | Built-in CC/CV with cell balancing |
+| Battery protection | Overcharge, overdischarge, short circuit, thermal |
+| Output usable voltage | USB-C PD (5V, 9V, 12V, 15V, 20V) |
+| Wall power input | USB-C input from any charger |
+| Charge while using | Passthrough charging |
+| Repairable | Bare PCB, cells are replaceable 18650s |
+
+## How It Works
+
+```
+USB-C wall charger → IP5389 board → 18650 cells (3S or 3S2P)
+                       ↓ (passthrough)
+              USB-C PD output → OPi5 (5V) + peripherals
+```
+
+One board, one cell pack, one output cable to the SBC. No separate modules to wire together.
+
+## Key Specs (varies by specific board)
+
+- Cell config: 3S–6S (most common: 3S or 4S)
+- Output: 45W–100W USB-C PD
+- Input: USB-C (bidirectional port)
+- Protection: overcharge, overdischarge, short circuit, thermal
+- Price: $8–15 bare PCB
+
+## Cell Configuration
+
+TBD — need to select specific board first. Likely 3S (3 cells in series) or 3S2P (6 cells, pairs in series). 3S2P with quality 3000mAh cells gives ~6000mAh at 11.1V nominal.
+
+## Salvaged Battery: Not Usable
+
+K501U battery (B31N1429, 4240mAh, 11.4V, 3S) assessed and rejected:
+- Integrated BMS is paired to the laptop mainboard
+- Most laptop BMS boards lock when removed from their system
+- Not worth the effort to hack around
+- Low capacity (4240mAh) doesn't justify the risk
+
+## Alternative Approaches Considered
+
+### Discrete Module Stack (TP5100 + 2S BMS + Buck Converter)
+- Three separate modules, more wiring
+- TP5100 charger (2S, 2A) + 2S 10A BMS + 5V/4A buck converter
+- ~$10 in modules, works well but more complex assembly
+- Backup plan if IP5389 board has issues
+
+### Commercial Power Bank (decased)
+- Buy a power bank, remove plastic shell, integrate bare PCB + cells
+- Zero design work but constrained to whatever cell layout the bank uses
+- Passthrough charging not guaranteed on all models
+
+### UPS HAT (Waveshare / DFRobot)
+- Designed for Raspberry Pi, works via USB output with OPi5
+- Premium price for unused GPIO header
+- Capped at 5V output, no 12V rail without extra boost converter
+
+## Safety Notes
+
+- Always use 18650 cells with matching capacity and age in parallel pairs
+- Fuse between board output and SBC (5A automotive blade fuse recommended)
+- No puffy, warm-at-rest, or sub-2.5V cells — ever
+- Match cell count to board specs (3S board = exactly 3S, don't mix)
+
+## TODO
+
+- [ ] Select specific IP5389 board model with verified reviews
+- [ ] Confirm cell count (3S vs 3S2P)
+- [ ] Verify passthrough charging on selected board
+- [ ] Order board + cells
+- [ ] Test charging and output before case integration