Add runtime UV protection toggle and treat near-zero sense as external power.

Per-pod NVS enable (default off) via UART/ESP-NOW/dashboard, and skip UV latch when LiPo ADC reads ~0 mV so USB/external supply still boots.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/README.md

@@ -121,6 +121,7 @@ Schema: `proto/esp_now_messages.proto`. Encode/decode: `esp_now_proto.c`. The ES
 | `ESPNOW_HEARTBEAT` | Slave → master | `EspNowSlavePresence` (same fields) |
 | `ESPNOW_SET_ACCEL_DEADZONE` | Master → slave | `EspNowAccelDeadzone` (`deadzone` LSB) |
 | `ESPNOW_SET_TAP_CONFIG` | Master → slave | `EspNowTapConfig` (multitap sens/timing/axis + enable S/D/T) |
+| `ESPNOW_SET_BATTERY_UV` | Master → slave | `EspNowBatteryUv` (runtime UV enable + clear latch when off) |
 | `ESPNOW_UNICAST_TEST` | Master → slave | `EspNowUnicastTest` (`seq`) |
 | `ESPNOW_FIND_ME` | Master → slave | `EspNowFindMe` (`client_id` filter) — LED locate sequence |
 | `ESPNOW_RESTART` | Master → slave | `EspNowRestart` (`client_id` filter) — reboot slave |
@@ -240,6 +241,7 @@ Host and master speak nanopb-encoded `UartMessage` inside UART frames (byte 0 =
 | 30 | `ESPNOW_ECHO_PING` | Implemented (`cmd/cmd_espnow_echo_ping.c`) — ESP-NOW timestamp echo (latency test) |
 | 31 | `SET_LOG_LEVEL` | Implemented (`cmd/cmd_set_log_level.c`) — get/set global `esp_log_level_set("*", …)` on master |
 | 32 | `TAP_CONFIG` | Implemented (`cmd/cmd_tap_config.c`) — get/set BMA456H multitap params (+ NVS) |
+| 36 | `BATTERY_UV` | Implemented (`cmd/cmd_battery_uv.c`) — get/set software UV enable (+ NVS / ESP-NOW) |
 
 Regenerate C code:
 
@@ -473,14 +475,17 @@ Read **cached** LiPo ADC values on the **master** (master local + one entry per
 
 ### Software UV protection (LiPo)
 
-When `POWERPOD_BATTERY_UV_ENABLE` is `1` (default in `powerpod.h`, disable via CMake), the firmware monitors ADC pin voltages on GPIO 1 and 11:
+When `POWERPOD_BATTERY_UV_ENABLE` is `1` (default in `powerpod.h`, disable via CMake), the firmware can monitor ADC pin voltages on GPIO 1 and 11. Runtime enable is NVS `uv_en` per pod (missing key → **disabled**); UART `BATTERY_UV` / dashboard toggles it on master and slaves.
 
 | Condition | ADC threshold | Action |
 |-----------|---------------|--------|
-| Under-voltage | any valid channel < **2300 mV** (3.0 V pack) | NVS latch `uv_latch`, restart into energy-save mode |
-| Charged | all valid channels ≥ **3000 mV** (4.0 V pack) | Clear latch, restart into normal boot |
+| External / absent | every valid channel < **100 mV** | Normal boot (no UV); clears latch if set |
+| Under-voltage | any valid channel in **100…2299 mV** | NVS latch `uv_latch`, restart into energy-save mode |
+| Charged | every non-absent valid channel ≥ **3000 mV** | Clear latch, restart into normal boot |
 
-**Energy-save boot:** LED mode `6` (first 4 LEDs red ~10 % for 5 s), then no WiFi/ESP-NOW, UART, I2C, BMA456, or button — only LiPo ADC polling every 30 s until charged.
+**Energy-save boot:** LED mode `6` (first 4 LEDs red ~10 % for 5 s), then no WiFi/ESP-NOW, UART, I2C, BMA456, or button — only LiPo ADC polling every 30 s until charged. Disabling UV while latched clears the latch (requires a reachable host — not while already in energy-save).
+
+**UART:** `BATTERY_UV` (`0x24`) — `client_id=0` master, `>0` one slave, `all_clients` master + all slaves. Disabling also clears `uv_latch`.
 
 **Test LED pattern from host:** `led-ring -mode battery-low` (works even when UV feature is disabled).
 
@@ -614,6 +619,7 @@ Target: ESP32-S3. Close serial monitor on the UART adapter port before running `
 | `pod_settings.c/h` | NVS persistence (accel deadzone, tap config, UV latch) |
 | `led_ring.c/h` | LED ring (digit display, progress bar) |
 | `cmd/cmd_led_ring.c` | UART `LED_RING` progress command |
+| `cmd/cmd_battery_uv.c` | UART `BATTERY_UV` — software UV enable + NVS / ESP-NOW |
 | `cmd/cmd_set_log_level.c` | UART `SET_LOG_LEVEL` — runtime ESP-IDF log level |
 | `proto/uart_messages.proto` | UART protocol schema |
 | `proto/esp_now_messages.proto` | ESP-NOW protocol schema |