Add BATT NOT FULL warning to OSD

Shows BATT NOT FULL when the connected battery has an everage cell
voltage of less than 0.2v lower then vbatmaxcellvoltage (when the craft
has yet to be armed)

Intended as a reminder to make sure pilots fly with a fresh battery

Adds an additional configuration option for the voltage at which a cell
is "full"

src/main/fc/settings.c

@@ -426,6 +426,7 @@ const clivalue_t valueTable[] = {
 // PG_BATTERY_CONFIG
     { "bat_capacity",               VAR_UINT16 | MASTER_VALUE, .config.minmax = { 0, 20000 }, PG_BATTERY_CONFIG, offsetof(batteryConfig_t, batteryCapacity) },
     { "vbat_max_cell_voltage",      VAR_UINT8  | MASTER_VALUE, .config.minmax = { 10, 50 }, PG_BATTERY_CONFIG, offsetof(batteryConfig_t, vbatmaxcellvoltage) },
+    { "vbat_full_cell_voltage",     VAR_UINT8  | MASTER_VALUE, .config.minmax = { 10, 50 }, PG_BATTERY_CONFIG, offsetof(batteryConfig_t, vbatfullcellvoltage) },
     { "vbat_min_cell_voltage",      VAR_UINT8  | MASTER_VALUE, .config.minmax = { 10, 50 }, PG_BATTERY_CONFIG, offsetof(batteryConfig_t, vbatmincellvoltage) },
     { "vbat_warning_cell_voltage",  VAR_UINT8  | MASTER_VALUE, .config.minmax = { 10, 50 }, PG_BATTERY_CONFIG, offsetof(batteryConfig_t, vbatwarningcellvoltage) },
     { "vbat_hysteresis",            VAR_UINT8  | MASTER_VALUE, .config.minmax = { 0, 250 }, PG_BATTERY_CONFIG, offsetof(batteryConfig_t, vbathysteresis) },

src/main/io/osd.c

@@ -596,6 +596,13 @@ static void osdDrawSingleElement(uint8_t item)
             break;
         }
 
+        /* Show warning if battery is not fresh */
+        if (!ARMING_FLAG(WAS_EVER_ARMED) && (getBatteryState() == BATTERY_OK)
+              && getBatteryAverageCellVoltage() < batteryConfig()->vbatfullcellvoltage) {
+            tfp_sprintf(buff, "BATT NOT FULL");
+            break;
+        }
+
         /* Show battery state warning */
         switch (getBatteryState()) {
         case BATTERY_WARNING:

src/main/sensors/battery.c

@@ -106,7 +106,9 @@ PG_RESET_TEMPLATE(batteryConfig_t, batteryConfig,
     .useVBatAlerts = true,
     .useConsumptionAlerts = false,
     .consumptionWarningPercentage = 10,
-    .vbathysteresis = 1
+    .vbathysteresis = 1,
+
+    .vbatfullcellvoltage = 41
 );
 
 void batteryUpdateVoltage(timeUs_t currentTimeUs)
@@ -462,6 +464,11 @@ uint8_t getBatteryCellCount(void)
     return batteryCellCount;
 }
 
+uint16_t getBatteryAverageCellVoltage(void)
+{
+    return voltageMeter.filtered / batteryCellCount;
+}
+
 int32_t getAmperage(void) {
     return currentMeter.amperage;
 }

src/main/sensors/battery.h

@@ -42,6 +42,8 @@ typedef struct batteryConfig_s {
     bool useConsumptionAlerts;              // Issue alerts based on total power consumption
     uint8_t consumptionWarningPercentage;   // Percentage of remaining capacity that should trigger a battery warning
     uint8_t vbathysteresis;                 // hysteresis for alarm, default 1 = 0.1V
+
+    uint8_t vbatfullcellvoltage;            // Cell voltage at which the battery is deemed to be "full" 0.1V units, default is 41 (4.1V)
    
 } batteryConfig_t;
 
@@ -77,6 +79,7 @@ uint8_t calculateBatteryPercentageRemaining(void);
 uint16_t getBatteryVoltage(void);
 uint16_t getBatteryVoltageLatest(void);
 uint8_t getBatteryCellCount(void);
+uint16_t getBatteryAverageCellVoltage(void);
 
 int32_t getAmperage(void);
 int32_t getAmperageLatest(void);

src/test/unit/osd_unittest.cc

@@ -648,6 +648,84 @@ TEST(OsdTest, TestElementAltitude)
     displayPortTestBufferSubstring(23, 7, "  -2.4%c", SYM_M);
 }
 
+/*
+ * Tests the battery notifications shown on the warnings OSD element.
+ */
+TEST(OsdTest, TestElementWarningsBattery)
+{
+    // given
+    osdConfigMutable()->item_pos[OSD_WARNINGS] = OSD_POS(9, 10) | VISIBLE_FLAG;
+
+    // and
+    batteryConfigMutable()->vbatfullcellvoltage = 41;
+
+    // and
+    // 4S battery
+    simulationBatteryCellCount = 4;
+
+    // and
+    // full battery
+    simulationBatteryVoltage = 168;
+    simulationBatteryState = BATTERY_OK;
+
+    // when
+    displayClearScreen(&testDisplayPort);
+    osdRefresh(simulationTime);
+
+    // then
+    displayPortTestBufferSubstring(9, 10, "           ");
+
+    // given
+    // low battery
+    simulationBatteryVoltage = 140;
+    simulationBatteryState = BATTERY_WARNING;
+
+    // when
+    displayClearScreen(&testDisplayPort);
+    osdRefresh(simulationTime);
+
+    // then
+    displayPortTestBufferSubstring(9, 10, "LOW BATTERY ");
+
+    // given
+    // crtical battery
+    simulationBatteryVoltage = 132;
+    simulationBatteryState = BATTERY_CRITICAL;
+
+    // when
+    displayClearScreen(&testDisplayPort);
+    osdRefresh(simulationTime);
+
+    // then
+    displayPortTestBufferSubstring(9, 10, " LAND NOW   ");
+
+    // given
+    // used battery
+    simulationBatteryVoltage = ((batteryConfig()->vbatmaxcellvoltage - 2) * simulationBatteryCellCount) - 1;
+    simulationBatteryState = BATTERY_OK;
+
+    // when
+    displayClearScreen(&testDisplayPort);
+    osdRefresh(simulationTime);
+
+    // then
+    displayPortTestBufferSubstring(9, 10, "BATT NOT FULL");
+
+    // given
+    // full battery
+    simulationBatteryVoltage = ((batteryConfig()->vbatmaxcellvoltage - 2) * simulationBatteryCellCount);
+    simulationBatteryState = BATTERY_OK;
+
+    // when
+    displayClearScreen(&testDisplayPort);
+    osdRefresh(simulationTime);
+
+    // then
+    displayPortTestBufferSubstring(9, 10, "             ");
+
+    // TODO
+}
+
 /*
  * Tests the time string formatting function with a series of precision settings and time values.
  */
@@ -744,6 +822,10 @@ extern "C" {
         return simulationBatteryVoltage;
     }
 
+    uint16_t getBatteryAverageCellVoltage() {
+        return simulationBatteryVoltage / simulationBatteryCellCount;
+    }
+
     int32_t getAmperage() {
         return simulationBatteryAmperage;
     }