Average battery ADC samples

- Read battery 5 times and average for a steadier voltage estimate

README.md

@@ -261,7 +261,7 @@ inline constexpr uint16_t EXPECTED_SENDER_IDS[NUM_SENDERS] = { 0xF19C };
   - 4.2 V = 100%
 - Uses deep sleep between cycles (`SENDER_WAKE_INTERVAL_SEC`).
 - Sender CPU is throttled to 80 MHz and LoRa RX is only enabled in short windows (ACK wait or time-sync).
-- Battery sampling uses a single ADC read and updates at most once per `BATTERY_SAMPLE_INTERVAL_MS` (default 60s).
+- Battery sampling averages 5 ADC reads and updates at most once per `BATTERY_SAMPLE_INTERVAL_MS` (default 60s).
 
 ## Web UI
 - AP SSID: `DD3-Bridge-<short_id>` (prefix configurable)

src/power_manager.cpp

@@ -34,8 +34,12 @@ void power_configure_unused_pins_sender() {
 }
 
 void read_battery(MeterData &data) {
-  uint32_t raw = analogRead(PIN_BAT_ADC);
-  float v = (static_cast<float>(raw) / 4095.0f) * ADC_REF_V * BATTERY_DIVIDER * BATTERY_CAL;
+  uint32_t sum = 0;
+  for (uint8_t i = 0; i < 5; ++i) {
+    sum += analogRead(PIN_BAT_ADC);
+  }
+  float avg = static_cast<float>(sum) / 5.0f;
+  float v = (avg / 4095.0f) * ADC_REF_V * BATTERY_DIVIDER * BATTERY_CAL;
 
   data.battery_voltage_v = v;
   data.battery_percent = battery_percent_from_voltage(v);