The Aegis-Beacon is designed for ultra-low power consumption. Deep sleep at 10 microamps enables 65+ hours of beacon operation on a single 18650 cell.

Power Sources

Battery

Parameter	Value
Type	18650 Li-ion
Voltage	3.7V nominal
Capacity	2600-3500 mAh
Recommended	LiFePO4 for alpine

Charging

Parameter	Value
Charger	TP4056 USB-C
Max Current	1A
Protection	DW01A (over-discharge)
LED Indicators	Red = charging, Blue = full

Current Consumption

By State

State	Current	Notes
Deep Sleep	~10 uA	ESP32 + RTC
TX Active (+17 dBm)	~120 mA	SX1262 + ESP32
TX Active (+22 dBm)	~150 mA	Max power
SEARCH Scan (RX)	~40 mA	SX1262 receive
WiFi AP (CONFIG)	~100 mA	ESP32 WiFi
OLED Active	~6 mA	SSD1309 display
OLED Power Save	~0.3 mA	setPowerSave(1)
GPS Acquiring	~30 mA	NEO-6M cold start
GPS Tracking	~25 mA	NEO-6M locked
Battery Divider	~0.021 mA	Always on
LEDs (each)	~2 mA	Red or Blue

Total Power Budget

BEACON Mode (10s sleep, GPS off):

CODE

Sleep: 10uA x 9.9s = 0.099 mA x s
TX: 120mA x 0.1s = 12 mA x s
OLED: 6mA x 0.1s = 0.6 mA x s
Total per cycle: 12.7 mA x s / 10s = 1.27 mA average

Estimated runtime (2000 mAh): ~65 hours

Battery Monitor

Hardware

Voltage divider on GPIO 36:

CODE

TP4056 BAT+ --> R3a (100k) --> GPIO 36 --> R3b (100k) --> GND

Divider ratio: VBAT / 2

ADC Configuration

CODE

// 32-sample averaging
uint32_t readBatteryADC() {
  uint32_t sum = 0;
  for (int i = 0; i < BAT_SAMPLES; i++) {
    sum += analogRead(BAT_PIN);
    delayMicroseconds(100);
  }
  return sum / BAT_SAMPLES;
}

Li-ion Discharge Curve

Voltage	Percentage
4.20V	100%
4.05V	90%
3.90V	75%
3.75V	60%
3.65V	50%
3.55V	35%
3.40V	20%
3.20V	10%
3.00V	0%

Calibration

If readings differ from multimeter:

CODE

#define BAT_VREF_MV   3900   // Adjust as needed

Charging Detection

Optional connection from TP4056 STDBY: not supported by the current pin map (GPIO 39 is the radio DIO1 line); charge state is judged from the percentage trend.

CODE

bool isCharging() {
  return digitalRead(CHG_PIN) == LOW; // LOW = charging
}

Tip

Charging detection is optional. Battery percentage works without it.

Runtime Estimates

BEACON Mode

Sleep Interval	GPS	OLED	Runtime
10s	Off	On	~65 hours
10s	On	On	~45 hours
30s	Off	On	~130 hours
60s	Off	On	~175 hours

SEARCH Mode

Configuration	Runtime
Continuous scan, GPS off	~44 hours
Continuous scan, GPS on	~30 hours

EMERGENCY Mode

Configuration	Runtime
Continuous TX, GPS on	~12 hours

Warning

At -20C with standard Li-ion, expect 40-60% of these figures. Use LiFePO4 for alpine deployments (rated to -30C).

Power Saving Features

WiFi/BT Shutdown

In BEACON and SEARCH modes:

CODE

WiFi.mode(WIFI_OFF);
btStop();
// Saves ~120 mA continuous draw

OLED Power Save

Before deep sleep:

CODE

u8g2.setPowerSave(1); // Turn off display
esp_deep_sleep(sleepTimeUs);

Radio Standby

After transmission:

CODE

radio.standby(); // Low power mode
// vs radio.sleep() // Even lower, but slower wakeup

Cold Weather Considerations

Battery Performance

Temperature	Capacity	Internal Resistance
20C	100%	1x
0C	80-90%	1.5x
-10C	60-80%	2x
-20C	40-60%	3x
-30C	20-40% (Li-ion)	5x

Recommendations

Use LiFePO4 cells (rated to -30C)
Keep device warm in pocket until needed
Reduce sleep interval for faster beacon rate
Replace electrolytic C1 with X7R ceramic below -10C

Tip

LiFePO4 cells have slightly lower capacity (1500-2000 mAh) but maintain performance in extreme cold.