2 files changed, 26 insertions, 11 deletions
diff --git a/src/components/battery/BatteryController.cpp b/src/components/battery/BatteryController.cpp
index 300d0978..4d860490 100644
--- a/src/components/battery/BatteryController.cpp
+++ b/src/components/battery/BatteryController.cpp
@@ -1,4 +1,5 @@
 #include "components/battery/BatteryController.h"
+#include "components/utility/LinearApproximation.h"
 #include "drivers/PinMap.h"
 #include <hal/nrf_gpio.h>
 #include <nrfx_saadc.h>
@@ -15,8 +16,8 @@ Battery::Battery() {
 }
 
 void Battery::ReadPowerState() {
-  isCharging = !nrf_gpio_pin_read(PinMap::Charging);
-  isPowerPresent = !nrf_gpio_pin_read(PinMap::PowerPresent);
+  isCharging = (nrf_gpio_pin_read(PinMap::Charging) == 0);
+  isPowerPresent = (nrf_gpio_pin_read(PinMap::PowerPresent) == 0);
 
   if (isPowerPresent && !isCharging) {
     isFull = true;
@@ -60,8 +61,8 @@ void Battery::SaadcInit() {
 }
 
 void Battery::SaadcEventHandler(nrfx_saadc_evt_t const* p_event) {
-  const uint16_t battery_max = 4180; // maximum voltage of battery ( max charging voltage is 4.21 )
-  const uint16_t battery_min = 3200; // minimum voltage of battery before shutdown ( depends on the battery )
+  static const Utility::LinearApproximation<uint16_t, uint8_t, 6> approx {
+    {{{3500, 0}, {3616, 3}, {3723, 22}, {3776, 48}, {3979, 79}, {4180, 100}}}};
 
   if (p_event->type == NRFX_SAADC_EVT_DONE) {
 
@@ -74,19 +75,26 @@ void Battery::SaadcEventHandler(nrfx_saadc_evt_t const* p_event) {
     // p_event->data.done.p_buffer[0] = (adc_voltage / reference_voltage) * 1024
     voltage = p_event->data.done.p_buffer[0] * (8 * 600) / 1024;
 
-    uint8_t newPercent;
-    if (isFull) {
-      newPercent = 100;
-    } else if (voltage < battery_min) {
-      newPercent = 0;
-    } else {
-      newPercent = std::min((voltage - battery_min) * 100 / (battery_max - battery_min), isCharging ? 99 : 100);
+    uint8_t newPercent = 100;
+    if (!isFull) {
+      // max. voltage while charging is higher than when discharging
+      newPercent = std::min(approx.GetValue(voltage), isCharging ? uint8_t {99} : uint8_t {100});
+    }
+
+    if (isPowerPresent) {
+      batteryLowNotified = false;
     }
 
     if ((isPowerPresent && newPercent > percentRemaining) || (!isPowerPresent && newPercent < percentRemaining) || firstMeasurement) {
       firstMeasurement = false;
       percentRemaining = newPercent;
       systemTask->PushMessage(System::Messages::BatteryPercentageUpdated);
+
+      // warn about low battery when not charging and below threshold
+      if (BatteryIsLow() && !isPowerPresent && !batteryLowNotified) {
+        systemTask->PushMessage(System::Messages::LowBattery);
+        batteryLowNotified = true;
+      }
     }
 
     nrfx_saadc_uninit();
diff --git a/src/components/battery/BatteryController.h b/src/components/battery/BatteryController.h
index 5a7394c4..b47b77cc 100644
--- a/src/components/battery/BatteryController.h
+++ b/src/components/battery/BatteryController.h
@@ -18,6 +18,10 @@ namespace Pinetime {
         return percentRemaining;
       }
 
+      bool BatteryIsLow() const {
+        return percentRemaining <= lowBatteryThreshold;
+      }
+
       uint16_t Voltage() const {
         return voltage;
       }
@@ -39,6 +43,7 @@ namespace Pinetime {
       static constexpr nrf_saadc_input_t batteryVoltageAdcInput = NRF_SAADC_INPUT_AIN7;
       uint16_t voltage = 0;
       uint8_t percentRemaining = 0;
+      bool batteryLowNotified = false;
 
       bool isFull = false;
       bool isCharging = false;
@@ -50,6 +55,8 @@ namespace Pinetime {
       void SaadcEventHandler(nrfx_saadc_evt_t const* p_event);
       static void AdcCallbackStatic(nrfx_saadc_evt_t const* event);
 
+      static constexpr uint8_t lowBatteryThreshold {15};
+
       bool isReading = false;
 
       Pinetime::System::SystemTask* systemTask = nullptr;