diff --git a/.gitignore b/.gitignore
index ae506da..77d82c0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -18,3 +18,12 @@
 .platformio_local/
 
 .codex
+
+
+exercises/09_GPS_Time/Doxyfile
+exercises/09_GPS_Time/Doxyfile_ORIG
+exercises/09_GPS_Time/html/
+exercises/18_GPS_Field_QA/lib/field_qa/BatteryMonitor.cpp
+exercises/18_GPS_Field_QA/lib/field_qa/BatteryMonitor.h
+exercises/AMY.log
+exercises/AMY_purged.log
diff --git a/exercises/18_GPS_Field_QA/lib/field_qa/Config.h b/exercises/18_GPS_Field_QA/lib/field_qa/Config.h
index c15297a..3546029 100644
--- a/exercises/18_GPS_Field_QA/lib/field_qa/Config.h
+++ b/exercises/18_GPS_Field_QA/lib/field_qa/Config.h
@@ -46,6 +46,10 @@
 #define FW_BUILD_UTC unknown
 #endif
 
+#ifndef LOG_AP_IP_OCTET
+#define LOG_AP_IP_OCTET 23
+#endif
+
 #define FIELD_QA_STR_INNER(x) #x
 #define FIELD_QA_STR(x) FIELD_QA_STR_INNER(x)
 
@@ -59,7 +63,7 @@ static constexpr const char* kStorageName = "SD";
 static constexpr const char* kLogDir = "/logs";
 static constexpr const char* kLogApPrefix = "GPSQA-";
 static constexpr const char* kLogApPassword = "";
-static constexpr uint8_t kLogApIpOctet = 23;
+static constexpr uint8_t kLogApIpOctet = LOG_AP_IP_OCTET;
 static constexpr uint32_t kSerialDelayMs = 4000;
 static constexpr uint32_t kSamplePeriodMs = 1000;
 static constexpr uint32_t kLogFlushPeriodMs = 10000;
diff --git a/exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.cpp b/exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.cpp
index 4a3cc42..d529263 100644
--- a/exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.cpp
+++ b/exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.cpp
@@ -21,6 +21,8 @@ void DisplayManager::begin() {
   Wire.begin(OLED_SDA, OLED_SCL);
   m_oled.setI2CAddress(OLED_ADDR << 1);
   m_oled.begin();
+  m_oled.setPowerSave(0);
+  m_powerSave = false;
 }
 
 void DisplayManager::drawLines(const char* l1,
@@ -40,15 +42,24 @@ void DisplayManager::drawLines(const char* l1,
   m_oled.sendBuffer();
 }
 
-void DisplayManager::showBoot(const char* line2, const char* line3) {
-  drawLines(kExerciseName, kFirmwareVersion, line2, line3);
+void DisplayManager::showBoot(const char* line2, const char* line3, const char* line4, const char* batteryText) {
+  char header[24];
+  if (batteryText && batteryText[0] != '\0') {
+    snprintf(header, sizeof(header), "%s %s", kExerciseName, batteryText);
+    drawLines(header, kFirmwareVersion, line2, line3, line4);
+  } else {
+    drawLines(kExerciseName, kFirmwareVersion, line2, line3, line4);
+  }
 }
 
 void DisplayManager::showError(const char* line1, const char* line2) {
   drawLines(kExerciseName, "ERROR", line1, line2);
 }
 
-void DisplayManager::showSample(const GnssSample& sample, const RunStats& stats, bool recording) {
+void DisplayManager::showSample(const GnssSample& sample,
+                                const RunStats& stats,
+                                bool recording,
+                                const char* batteryText) {
   char l1[24];
   char l2[20];
   char l3[20];
@@ -56,7 +67,11 @@ void DisplayManager::showSample(const GnssSample& sample, const RunStats& stats,
   char l5[20];
   char l6[20];
 
-  snprintf(l1, sizeof(l1), "%s", recording ? "*RECORDING" : "Halted");
+  snprintf(l1,
+           sizeof(l1),
+           "%s %s",
+           recording ? "*RECORDING" : "Halted",
+           (batteryText && batteryText[0] != '\0') ? batteryText : "--.-v");
   snprintf(l2, sizeof(l2), "FIX: %s", fixTypeToString(sample.fixType));
   snprintf(l3, sizeof(l3), "USED: %d/%d", sample.satsUsed < 0 ? 0 : sample.satsUsed, sample.satsInView < 0 ? 0 : sample.satsInView);
   if (sample.validHdop) {
@@ -69,4 +84,16 @@ void DisplayManager::showSample(const GnssSample& sample, const RunStats& stats,
   drawLines(l1, l2, l3, l4, l5, l6);
 }
 
+void DisplayManager::setPowerSave(bool enabled) {
+  if (m_powerSave == enabled) {
+    return;
+  }
+  m_oled.setPowerSave(enabled ? 1 : 0);
+  m_powerSave = enabled;
+}
+
+bool DisplayManager::powerSave() const {
+  return m_powerSave;
+}
+
 }  // namespace field_qa
diff --git a/exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.h b/exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.h
index 2859675..5c66596 100644
--- a/exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.h
+++ b/exercises/18_GPS_Field_QA/lib/field_qa/DisplayManager.h
@@ -10,9 +10,14 @@ namespace field_qa {
 class DisplayManager {
  public:
   void begin();
-  void showBoot(const char* line2, const char* line3 = nullptr);
+  void showBoot(const char* line2,
+                const char* line3 = nullptr,
+                const char* line4 = nullptr,
+                const char* batteryText = nullptr);
   void showError(const char* line1, const char* line2 = nullptr);
-  void showSample(const GnssSample& sample, const RunStats& stats, bool recording);
+  void showSample(const GnssSample& sample, const RunStats& stats, bool recording, const char* batteryText);
+  void setPowerSave(bool enabled);
+  bool powerSave() const;
 
  private:
   void drawLines(const char* l1,
@@ -23,6 +28,7 @@ class DisplayManager {
                  const char* l6 = nullptr);
 
   U8G2_SH1106_128X64_NONAME_F_HW_I2C m_oled{U8G2_R0, U8X8_PIN_NONE};
+  bool m_powerSave = false;
 };
 
 }  // namespace field_qa
diff --git a/exercises/18_GPS_Field_QA/lib/field_qa/StorageManager.cpp b/exercises/18_GPS_Field_QA/lib/field_qa/StorageManager.cpp
index d368233..8a4471a 100644
--- a/exercises/18_GPS_Field_QA/lib/field_qa/StorageManager.cpp
+++ b/exercises/18_GPS_Field_QA/lib/field_qa/StorageManager.cpp
@@ -265,13 +265,14 @@ bool StorageManager::appendLine(const String& line) {
   return appendBytes(record.c_str(), record.length());
 }
 
-void StorageManager::appendSampleCsv(const GnssSample& sample,
+bool StorageManager::appendSampleCsv(const GnssSample& sample,
                                      uint32_t sampleSeq,
                                      uint32_t msSinceRunStart,
                                      const char* runId,
                                      const char* bootTimestampUtc) {
   if (!m_file) {
-    return;
+    m_lastError = "log file not open";
+    return false;
   }
   if (m_file.size() == 0) {
     writeHeader(runId, bootTimestampUtc);
@@ -350,10 +351,10 @@ void StorageManager::appendSampleCsv(const GnssSample& sample,
   line += kLogFieldDelimiter;
   line += String(sample.longestNoFixMs);
   line += ",,,,,,,";
-  (void)appendLine(line);
+  return appendLine(line);
 }
 
-void StorageManager::appendSatelliteCsv(const GnssSample& sample,
+bool StorageManager::appendSatelliteCsv(const GnssSample& sample,
                                         uint32_t sampleSeq,
                                         uint32_t msSinceRunStart,
                                         const SatelliteInfo* satellites,
@@ -361,7 +362,10 @@ void StorageManager::appendSatelliteCsv(const GnssSample& sample,
                                         const char* runId,
                                         const char* bootTimestampUtc) {
   if (!satellites || satelliteCount == 0 || !m_file) {
-    return;
+    if (!m_file) {
+      m_lastError = "log file not open";
+    }
+    return false;
   }
   if (m_file.size() == 0) {
     writeHeader(runId, bootTimestampUtc);
@@ -458,26 +462,30 @@ void StorageManager::appendSatelliteCsv(const GnssSample& sample,
     line += String(sat.snr);
     line += kLogFieldDelimiter;
     line += sat.usedInSolution ? "1" : "0";
-    (void)appendLine(line);
+    if (!appendLine(line)) {
+      return false;
+    }
   }
+  return true;
 }
 
-void StorageManager::flush() {
+bool StorageManager::flush() {
   if (!m_file) {
-    return;
+    return false;
   }
 
   if (m_bufferLengths[m_activeBuffer] > 0) {
     m_bufferPending[m_activeBuffer] = true;
   }
   if (!writePendingBuffer()) {
-    return;
+    return false;
   }
   m_file.flush();
+  return true;
 }
 
 void StorageManager::close() {
-  flush();
+  (void)flush();
   if (m_file) {
     m_file.close();
   }
diff --git a/exercises/18_GPS_Field_QA/lib/field_qa/StorageManager.h b/exercises/18_GPS_Field_QA/lib/field_qa/StorageManager.h
index 5acf8cf..9645284 100644
--- a/exercises/18_GPS_Field_QA/lib/field_qa/StorageManager.h
+++ b/exercises/18_GPS_Field_QA/lib/field_qa/StorageManager.h
@@ -17,19 +17,19 @@ class StorageManager {
   bool fileOpen() const;
   size_t bufferedBytes() const;
   size_t logFileCount() const;
-  void appendSampleCsv(const GnssSample& sample,
+  bool appendSampleCsv(const GnssSample& sample,
                        uint32_t sampleSeq,
                        uint32_t msSinceRunStart,
                        const char* runId,
                        const char* bootTimestampUtc);
-  void appendSatelliteCsv(const GnssSample& sample,
+  bool appendSatelliteCsv(const GnssSample& sample,
                           uint32_t sampleSeq,
                           uint32_t msSinceRunStart,
                           const SatelliteInfo* satellites,
                           size_t satelliteCount,
                           const char* runId,
                           const char* bootTimestampUtc);
-  void flush();
+  bool flush();
   void close();
   void listFiles(Stream& out);
   void catFile(Stream& out, const char* path);
diff --git a/exercises/18_GPS_Field_QA/platformio.ini b/exercises/18_GPS_Field_QA/platformio.ini
index 49c13ea..2b8980b 100644
--- a/exercises/18_GPS_Field_QA/platformio.ini
+++ b/exercises/18_GPS_Field_QA/platformio.ini
@@ -40,6 +40,7 @@ build_flags =
   -D NODE_LABEL=\"Amy\"
   -D NODE_SHORT=\"A\"
   -D NODE_SLOT_INDEX=0
+  -D LOG_AP_IP_OCTET=23
   -D GNSS_CHIP_NAME=\"L76K\"
 
 [env:bob]
@@ -50,6 +51,7 @@ build_flags =
   -D NODE_LABEL=\"Bob\"
   -D NODE_SHORT=\"B\"
   -D NODE_SLOT_INDEX=1
+  -D LOG_AP_IP_OCTET=24
   -D GNSS_CHIP_NAME=\"L76K\"
 
 [env:cy]
@@ -60,6 +62,7 @@ build_flags =
   -D NODE_LABEL=\"Cy\"
   -D NODE_SHORT=\"C\"
   -D NODE_SLOT_INDEX=2
+  -D LOG_AP_IP_OCTET=25
   -D GNSS_CHIP_NAME=\"L76K\"
 
 [env:dan]
@@ -70,6 +73,7 @@ build_flags =
   -D NODE_LABEL=\"Dan\"
   -D NODE_SHORT=\"D\"
   -D NODE_SLOT_INDEX=3
+  -D LOG_AP_IP_OCTET=26
   -D GNSS_CHIP_NAME=\"L76K\"
 
 [env:ed]
@@ -80,6 +84,7 @@ build_flags =
   -D NODE_LABEL=\"Ed\"
   -D NODE_SHORT=\"E\"
   -D NODE_SLOT_INDEX=4
+  -D LOG_AP_IP_OCTET=27
   -D GNSS_CHIP_NAME=\"L76K\"
 
 [env:flo]
@@ -90,6 +95,7 @@ build_flags =
   -D NODE_LABEL=\"Flo\"
   -D NODE_SHORT=\"F\"
   -D NODE_SLOT_INDEX=5
+  -D LOG_AP_IP_OCTET=28
   -D GNSS_CHIP_NAME=\"L76K\"
 
 [env:guy]
@@ -100,5 +106,6 @@ build_flags =
   -D NODE_LABEL=\"Guy\"
   -D NODE_SHORT=\"G\"
   -D NODE_SLOT_INDEX=6
+  -D LOG_AP_IP_OCTET=29
   -D GNSS_CHIP_NAME=\"MAX-M10S\"
   -D GPS_UBLOX
diff --git a/exercises/18_GPS_Field_QA/src/main.cpp b/exercises/18_GPS_Field_QA/src/main.cpp
index 3b515d8..5c7b179 100644
--- a/exercises/18_GPS_Field_QA/src/main.cpp
+++ b/exercises/18_GPS_Field_QA/src/main.cpp
@@ -5,11 +5,13 @@
 #include <ctype.h>
 #include <SPI.h>
 #include <SD.h>
+#include <stdarg.h>
 #include <strings.h>
 #include <Wire.h>
 #include <WiFi.h>
 #include <WebServer.h>
 
+#include "BatteryMonitor.h"
 #include "ClockDiscipline.h"
 #include "Config.h"
 #include "DisplayManager.h"
@@ -27,6 +29,7 @@ XPowersLibInterface* g_pmu = nullptr;
 DisplayManager g_display;
 GnssManager g_gnss;
 ClockDiscipline g_clock;
+BatteryMonitor g_battery;
 StorageManager g_storage;
 RunStats g_stats;
 StartupSdManager g_sd(Serial);
@@ -53,6 +56,9 @@ bool g_buttonHoldHandled = false;
 uint32_t g_buttonPressedMs = 0;
 uint32_t g_buttonConfirmDeadlineMs = 0;
 uint32_t g_buttonStopMessageUntilMs = 0;
+char g_lastHaltReason[32] = "none";
+bool g_displayAutoSleepEnabled = false;
+uint32_t g_displayWakeUntilMs = 0;
 
 uint32_t g_lastSampleMs = 0;
 uint32_t g_lastFlushMs = 0;
@@ -64,11 +70,66 @@ volatile uint32_t g_ppsEdgeCount = 0;
 static constexpr uint32_t kButtonHoldPromptMs = 1500;
 static constexpr uint32_t kButtonConfirmWindowMs = 3000;
 static constexpr uint32_t kButtonStopMessageMs = 4000;
+static constexpr uint32_t kDisplayWakeMs = 120000;
+static constexpr size_t kEventLogCapacity = 128;
+static constexpr size_t kEventLogLineBytes = 96;
+char g_eventLog[kEventLogCapacity][kEventLogLineBytes] = {};
+size_t g_eventLogHead = 0;
+size_t g_eventLogCount = 0;
 
 void IRAM_ATTR onPpsEdge() {
   ++g_ppsEdgeCount;
 }
 
+String htmlEscape(const String& in);
+
+void recordEvent(const char* fmt, ...) {
+  char msg[72];
+  va_list args;
+  va_start(args, fmt);
+  vsnprintf(msg, sizeof(msg), fmt, args);
+  va_end(args);
+
+  char line[kEventLogLineBytes];
+  snprintf(line, sizeof(line), "%10lu %s", (unsigned long)millis(), msg);
+  strlcpy(g_eventLog[g_eventLogHead], line, sizeof(g_eventLog[g_eventLogHead]));
+  g_eventLogHead = (g_eventLogHead + 1) % kEventLogCapacity;
+  if (g_eventLogCount < kEventLogCapacity) {
+    ++g_eventLogCount;
+  }
+  Serial.printf("EVENT: %s\n", msg);
+}
+
+void setLastHaltReason(const char* reason) {
+  strlcpy(g_lastHaltReason, (reason && reason[0] != '\0') ? reason : "none", sizeof(g_lastHaltReason));
+}
+
+void wakeDisplay(uint32_t durationMs = kDisplayWakeMs) {
+  g_display.setPowerSave(false);
+  g_displayWakeUntilMs = millis() + durationMs;
+}
+
+void updateDisplayPowerState() {
+  if (!g_displayAutoSleepEnabled) {
+    g_display.setPowerSave(false);
+    return;
+  }
+  if ((int32_t)(millis() - g_displayWakeUntilMs) >= 0) {
+    g_display.setPowerSave(true);
+  }
+}
+
+void appendRecentEventsHtml(String& html) {
+  html += "<h2>Recent Events</h2><pre>";
+  const size_t start = (g_eventLogCount < kEventLogCapacity) ? 0 : g_eventLogHead;
+  for (size_t i = 0; i < g_eventLogCount; ++i) {
+    const size_t idx = (start + i) % kEventLogCapacity;
+    html += htmlEscape(String(g_eventLog[idx]));
+    html += "\n";
+  }
+  html += "</pre>";
+}
+
 String htmlEscape(const String& in) {
   String out;
   out.reserve(in.length() + 16);
@@ -151,6 +212,8 @@ void printSummary() {
   Serial.printf("storage_used_bytes=%u\n", g_storageMounted ? (unsigned)SD.usedBytes() : 0U);
   Serial.printf("storage_buffered_bytes=%u\n", (unsigned)g_storage.bufferedBytes());
   Serial.printf("storage_log_count=%u\n", (unsigned)g_logFileCount);
+  Serial.printf("halt_reason=%s\n", g_lastHaltReason);
+  Serial.printf("battery_voltage=%s\n", g_battery.voltageText());
   Serial.printf("web_ready=%s\n", g_webReady ? "yes" : "no");
   Serial.printf("web_url=http://192.168.%u.1/\n", (unsigned)kLogApIpOctet);
 }
@@ -207,7 +270,11 @@ bool ensureStorageReady() {
   g_sampleSeq = 0;
   g_runStartMs = millis();
   g_loggingEnabled = true;
+  setLastHaltReason("none");
+  g_displayAutoSleepEnabled = true;
+  wakeDisplay();
   g_logFileCount = g_storage.logFileCount();
+  recordEvent("logging_started path=%s", g_storage.currentPath());
   Serial.printf("logging started: %s\n", g_storage.currentPath());
   return true;
 }
@@ -216,10 +283,14 @@ void stopLoggingCleanly(const char* reason) {
   if (!g_loggingEnabled && !g_storageReady) {
     return;
   }
-  g_storage.flush();
+  (void)g_storage.flush();
   g_storage.close();
   g_storageReady = false;
   g_loggingEnabled = false;
+  setLastHaltReason(reason);
+  g_displayAutoSleepEnabled = true;
+  wakeDisplay();
+  recordEvent("logging_stopped reason=%s", g_lastHaltReason);
   if (reason && reason[0] != '\0') {
     Serial.printf("logging stopped: %s\n", reason);
   } else {
@@ -228,16 +299,36 @@ void stopLoggingCleanly(const char* reason) {
   g_buttonStopMessageUntilMs = millis() + kButtonStopMessageMs;
 }
 
+void stopLoggingForStorageFailure(const char* phase) {
+  g_storageReady = false;
+  g_loggingEnabled = false;
+  setLastHaltReason("sd_write_failed");
+  g_displayAutoSleepEnabled = true;
+  wakeDisplay();
+  recordEvent("sd_write_failed phase=%s err=%s",
+              phase ? phase : "unknown",
+              g_storage.lastError()[0] ? g_storage.lastError() : "none");
+  Serial.printf("ERROR: sd_write_failed phase=%s err=%s\n",
+                phase ? phase : "unknown",
+                g_storage.lastError()[0] ? g_storage.lastError() : "none");
+  g_buttonStopMessageUntilMs = millis() + kButtonStopMessageMs;
+}
+
 bool rescanSdCard() {
-  g_storage.flush();
+  recordEvent("sd_rescan requested");
+  (void)g_storage.flush();
   g_storage.close();
   g_storageReady = false;
   g_loggingEnabled = false;
   const bool mounted = g_sd.forceRemount();
   g_storageMounted = g_sd.isMounted();
+  wakeDisplay();
   if (mounted) {
+    recordEvent("sd_rescan mounted");
     g_sd.printCardInfo();
     (void)ensureStorageReady();
+  } else {
+    recordEvent("sd_rescan failed");
   }
   return mounted;
 }
@@ -246,6 +337,10 @@ void pollStopButton() {
   const uint32_t now = millis();
   const bool pressed = (digitalRead(BUTTON_PIN) == LOW);
 
+  if (pressed) {
+    wakeDisplay();
+  }
+
   if (g_buttonConfirmActive && (int32_t)(now - g_buttonConfirmDeadlineMs) >= 0) {
     g_buttonConfirmActive = false;
   }
@@ -254,7 +349,7 @@ void pollStopButton() {
     g_buttonPressedMs = now;
     g_buttonHoldHandled = false;
     if (g_buttonConfirmActive && g_loggingEnabled) {
-      stopLoggingCleanly("button confirm");
+      stopLoggingCleanly("button_confirm");
       g_buttonConfirmActive = false;
     }
   } else if (pressed && !g_buttonHoldHandled && !g_buttonConfirmActive && g_loggingEnabled &&
@@ -262,7 +357,8 @@ void pollStopButton() {
     g_buttonHoldHandled = true;
     g_buttonConfirmActive = true;
     g_buttonConfirmDeadlineMs = now + kButtonConfirmWindowMs;
-    g_display.showBoot("Stop recording?", "Press again in 3s");
+    recordEvent("button_prompt stop_recording");
+    g_display.showBoot("Stop recording?", "Press again in 3s", nullptr, g_battery.voltageText());
   }
 
   if (!pressed && g_buttonPrevPressed) {
@@ -276,11 +372,14 @@ void handleSdStateTransitions() {
   g_sd.update();
   if (g_sd.consumeMountedEvent()) {
     g_storageMounted = true;
+    recordEvent("sd_mounted");
     Serial.println("SD mounted");
     g_sd.printCardInfo();
     (void)ensureStorageReady();
   }
   if (g_sd.consumeRemovedEvent()) {
+    setLastHaltReason("sd_removed");
+    recordEvent("sd_removed");
     Serial.println("SD removed");
     g_storageMounted = false;
     g_storage.close();
@@ -314,6 +413,9 @@ void attemptClockDiscipline(const GnssSample& sample) {
 
   setRunIdentityFromClock(disciplinedUtc);
   g_clockDisciplined = true;
+  g_displayAutoSleepEnabled = true;
+  wakeDisplay();
+  recordEvent("clock_disciplined run_id=%s", g_runId);
   Serial.printf("RTC disciplined to GPS: %s", g_bootTimestampUtc);
   if (hadPriorRtc) {
     Serial.printf(" drift=%+llds", (long long)driftSeconds);
@@ -324,6 +426,7 @@ void attemptClockDiscipline(const GnssSample& sample) {
 }
 
 void sampleAndMaybeLog() {
+  g_battery.update(millis());
   GnssSample sample = g_gnss.makeSample();
   g_stats.updateFromSample(sample, millis());
   sample.ttffMs = g_stats.ttffMs();
@@ -336,8 +439,12 @@ void sampleAndMaybeLog() {
     const uint32_t msSinceRunStart = millis() - g_runStartMs;
     SatelliteInfo sats[kMaxSatellites];
     const size_t satCount = g_gnss.copySatellites(sats, kMaxSatellites);
-    g_storage.appendSampleCsv(sample, sampleSeq, msSinceRunStart, g_runId, g_bootTimestampUtc);
-    g_storage.appendSatelliteCsv(sample, sampleSeq, msSinceRunStart, sats, satCount, g_runId, g_bootTimestampUtc);
+    if (!g_storage.appendSampleCsv(sample, sampleSeq, msSinceRunStart, g_runId, g_bootTimestampUtc)) {
+      stopLoggingForStorageFailure("append_sample");
+    } else if (satCount > 0 &&
+               !g_storage.appendSatelliteCsv(sample, sampleSeq, msSinceRunStart, sats, satCount, g_runId, g_bootTimestampUtc)) {
+      stopLoggingForStorageFailure("append_satellite");
+    }
   }
 
   if (g_periodicSerialEnabled && (uint32_t)(millis() - g_lastStatusMs) >= kStatusPeriodMs) {
@@ -348,16 +455,20 @@ void sampleAndMaybeLog() {
     g_lastDisplayMs = millis();
     if (g_clockDisciplined) {
       if (g_buttonConfirmActive) {
-        g_display.showBoot("Stop recording?", "Press again in 3s");
+        g_display.showBoot("Stop recording?", "Press again in 3s", nullptr, g_battery.voltageText());
       } else if ((uint32_t)(millis() - g_buttonStopMessageUntilMs) < kButtonStopMessageMs) {
-        g_display.showBoot("Halted", "Safe to power off");
-      } else {
-        g_display.showSample(sample, g_stats, g_loggingEnabled);
+        g_display.showBoot("Halted", g_lastHaltReason, "Safe to power off", g_battery.voltageText());
+      } else if (!g_display.powerSave()) {
+        g_display.showSample(sample, g_stats, g_loggingEnabled, g_battery.voltageText());
       }
     } else {
-      g_display.showBoot("Waiting for GPS UTC", sample.validTime ? "Awaiting PPS" : "No valid time yet");
+      g_display.showBoot("Waiting for GPS UTC",
+                         sample.validTime ? "Awaiting PPS" : "No valid time yet",
+                         nullptr,
+                         g_battery.voltageText());
     }
   }
+  updateDisplayPowerState();
 }
 
 void buildFileTreeHtml(String& html, const char* path) {
@@ -430,7 +541,7 @@ bool normalizeWebPath(const String& input, String& out) {
 }
 
 void handleWebIndex() {
-  g_storage.flush();
+  (void)g_storage.flush();
   String html;
   html.reserve(8192);
   html += "<!doctype html><html><head><meta charset='utf-8'><title>GPSQA ";
@@ -453,6 +564,10 @@ void handleWebIndex() {
   html += htmlEscape(String(g_storage.lastError()));
   html += "<br>Current log: ";
   html += htmlEscape(String(g_storage.currentPath()));
+  html += "<br>Halt reason: ";
+  html += htmlEscape(String(g_lastHaltReason));
+  html += "<br>Battery: ";
+  html += htmlEscape(String(g_battery.voltageText()));
   html += "</p>";
   html += "<p><a href='/cmd?status=1'>status</a> ";
   html += "<a href='/cmd?flush=1'>flush</a> ";
@@ -470,12 +585,13 @@ void handleWebIndex() {
 
   html += "</ul><p>Web commands also accept query forms like ";
   html += "<code>/cmd?erase=/logs/20260406_093912_CY.csv</code></p>";
+  appendRecentEventsHtml(html);
   html += "</body></html>";
   g_server.send(200, "text/html; charset=utf-8", html);
 }
 
 void handleWebDownload() {
-  g_storage.flush();
+  (void)g_storage.flush();
   String pathArg = g_server.hasArg("path") ? g_server.arg("path") : g_server.arg("name");
   String fullPath;
   if (!normalizeWebPath(pathArg, fullPath)) {
@@ -513,7 +629,7 @@ void handleWebCommand() {
   String response;
 
   if (g_server.hasArg("erase")) {
-    g_storage.flush();
+    (void)g_storage.flush();
     const String path = g_server.arg("erase");
     if (g_storage.eraseFile(path.c_str())) {
       g_storageReady = g_storage.ready();
@@ -526,7 +642,7 @@ void handleWebCommand() {
       response = String("erase failed: ") + g_storage.lastError();
     }
   } else if (g_server.hasArg("erase_logs")) {
-    g_storage.flush();
+    (void)g_storage.flush();
     g_storage.eraseLogs(Serial);
     g_storageReady = g_storage.ready();
     if (!g_storageReady) {
@@ -535,8 +651,7 @@ void handleWebCommand() {
     g_logFileCount = g_storage.logFileCount();
     response = "logs erased";
   } else if (g_server.hasArg("flush")) {
-    g_storage.flush();
-    response = "buffer flushed";
+    response = g_storage.flush() ? "buffer flushed" : String("flush failed: ") + g_storage.lastError();
   } else if (g_server.hasArg("stop")) {
     stopLoggingCleanly("web stop");
     response = "logging stopped";
@@ -566,6 +681,8 @@ void handleWebCommand() {
     response += g_storageReady ? "yes" : "no";
     response += "\nsd_state=";
     response += g_storageMounted ? "mounted" : "absent";
+    response += "\nhalt_reason=";
+    response += g_lastHaltReason;
   } else {
     response = "commands: status flush start stop sd_rescan erase=<path> erase_logs=1";
   }
@@ -700,9 +817,11 @@ void setup() {
     Serial.println("WARNING: PMU init failed");
   }
 
+  g_battery.begin(g_pmu);
   g_display.begin();
   pinMode(BUTTON_PIN, INPUT_PULLUP);
-  g_display.showBoot("Booting...", kBoardId);
+  wakeDisplay();
+  g_display.showBoot("Booting...", kBoardId, nullptr, g_battery.voltageText());
   g_stats.begin(millis());
   g_gnss.begin();
   (void)g_gnss.probeAtStartup(Serial);
@@ -731,8 +850,9 @@ void setup() {
     Serial.println("RTC invalid at boot");
   }
 
+  recordEvent("boot board=%s", kBoardId);
   printProvenance();
-  g_display.showBoot("Waiting for GPS UTC", "No log before RTC set");
+  g_display.showBoot("Waiting for GPS UTC", "No log before RTC set", nullptr, g_battery.voltageText());
 
   g_lastSampleMs = millis();
   g_lastFlushMs = millis();
@@ -752,6 +872,8 @@ void loop() {
   }
   if (g_storageReady && (uint32_t)(now - g_lastFlushMs) >= kLogFlushPeriodMs) {
     g_lastFlushMs = now;
-    g_storage.flush();
+    if (!g_storage.flush()) {
+      stopLoggingForStorageFailure("periodic_flush");
+    }
   }
 }