diff --git a/app/build.gradle b/app/build.gradle
index d105609a..34700ef1 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -17,14 +17,15 @@ android {
         minSdkVersion 14
         targetSdkVersion 24
 
-        versionCode 110
+        versionCode 111
 
         buildConfigField "long", "buildTime", System.currentTimeMillis() + "L"
+        buildConfigField "boolean", "useMTM", "true"
     }
 
     productFlavors {
         standard {
-            versionName "1.2.1-ose"
+            versionName "1.2.2-ose"
         }
     }
 
diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index f66723cc..215c06ed 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -19,6 +19,7 @@
     <uses-permission android:name="android.permission.MANAGE_ACCOUNTS"/>
     <uses-permission android:name="android.permission.READ_SYNC_SETTINGS"/>
     <uses-permission android:name="android.permission.WRITE_SYNC_SETTINGS"/>
+    <uses-permission android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS"/>
 
     <!-- legacy permissions -->
     <uses-permission
diff --git a/app/src/main/java/at/bitfire/davdroid/ui/AppSettingsActivity.java b/app/src/main/java/at/bitfire/davdroid/ui/AppSettingsActivity.java
index d44b672d..3dad59ea 100644
--- a/app/src/main/java/at/bitfire/davdroid/ui/AppSettingsActivity.java
+++ b/app/src/main/java/at/bitfire/davdroid/ui/AppSettingsActivity.java
@@ -75,6 +75,7 @@ public class AppSettingsActivity extends AppCompatActivity {
         private void resetHints() {
             @Cleanup ServiceDB.OpenHelper dbHelper = new ServiceDB.OpenHelper(getContext());
             Settings settings = new Settings(dbHelper.getWritableDatabase());
+            settings.remove(StartupDialogFragment.HINT_BATTERY_OPTIMIZATIONS);
             settings.remove(StartupDialogFragment.HINT_OPENTASKS_NOT_INSTALLED);
             Snackbar.make(getView(), R.string.app_settings_reset_hints_success, Snackbar.LENGTH_LONG).show();
         }
diff --git a/app/src/main/java/at/bitfire/davdroid/ui/StartupDialogFragment.java b/app/src/main/java/at/bitfire/davdroid/ui/StartupDialogFragment.java
index 095a2f3e..494416d4 100644
--- a/app/src/main/java/at/bitfire/davdroid/ui/StartupDialogFragment.java
+++ b/app/src/main/java/at/bitfire/davdroid/ui/StartupDialogFragment.java
@@ -17,6 +17,7 @@ import android.graphics.drawable.Drawable;
 import android.net.Uri;
 import android.os.Build;
 import android.os.Bundle;
+import android.os.PowerManager;
 import android.support.annotation.NonNull;
 import android.support.v4.app.DialogFragment;
 import android.support.v7.app.AlertDialog;
@@ -37,13 +38,17 @@ import lombok.Cleanup;
 
 public class StartupDialogFragment extends DialogFragment {
     public static final String
+            HINT_BATTERY_OPTIMIZATIONS = "hint_BatteryOptimizations",
+            HINT_GOOGLE_PLAY_ACCOUNTS_REMOVED = "hint_GooglePlayAccountsRemoved",
             HINT_OPENTASKS_NOT_INSTALLED = "hint_OpenTasksNotInstalled";
 
     private static final String ARGS_MODE = "mode";
 
     enum Mode {
+        BATTERY_OPTIMIZATIONS,
         DEVELOPMENT_VERSION,
         FDROID_DONATE,
+        GOOGLE_PLAY_ACCOUNTS_REMOVED,
         OPENTASKS_NOT_INSTALLED
     }
 
@@ -58,9 +63,15 @@ public class StartupDialogFragment extends DialogFragment {
         else
             dialogs.add(StartupDialogFragment.instantiate(Mode.FDROID_DONATE));
 
+        // battery optimization whitelisting
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && settings.getBoolean(HINT_BATTERY_OPTIMIZATIONS, true)) {
+            PowerManager powerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
+            if (!powerManager.isIgnoringBatteryOptimizations(BuildConfig.APPLICATION_ID))
+                dialogs.add(StartupDialogFragment.instantiate(Mode.BATTERY_OPTIMIZATIONS));
+        }
+
         // OpenTasks information
-        if (!LocalTaskList.tasksProviderAvailable(context) &&
-                settings.getBoolean(HINT_OPENTASKS_NOT_INSTALLED, true))
+        if (!LocalTaskList.tasksProviderAvailable(context) && settings.getBoolean(HINT_OPENTASKS_NOT_INSTALLED, true))
             dialogs.add(StartupDialogFragment.instantiate(Mode.OPENTASKS_NOT_INSTALLED));
 
         Collections.reverse(dialogs);
@@ -84,6 +95,32 @@ public class StartupDialogFragment extends DialogFragment {
 
         Mode mode = Mode.valueOf(getArguments().getString(ARGS_MODE));
         switch (mode) {
+            case BATTERY_OPTIMIZATIONS:
+                return new AlertDialog.Builder(getActivity())
+                        .setTitle(R.string.startup_battery_optimization)
+                        .setMessage(R.string.startup_battery_optimization_message)
+                        .setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
+                            @Override
+                            public void onClick(DialogInterface dialog, int which) {
+                            }
+                        })
+                        .setNeutralButton(R.string.startup_battery_optimization_disable, new DialogInterface.OnClickListener() {
+                            @Override
+                            public void onClick(DialogInterface dialog, int which) {
+                                Intent intent = new Intent(android.provider.Settings.ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS,
+                                        Uri.parse("package:" + BuildConfig.APPLICATION_ID));
+                                getContext().startActivity(intent);
+                            }
+                        })
+                        .setNegativeButton(R.string.startup_dont_show_again, new DialogInterface.OnClickListener() {
+                            @Override
+                            public void onClick(DialogInterface dialog, int which) {
+                                Settings settings = new Settings(dbHelper.getWritableDatabase());
+                                settings.putBoolean(HINT_BATTERY_OPTIMIZATIONS, false);
+                            }
+                        })
+                        .create();
+
             case DEVELOPMENT_VERSION:
                 return new AlertDialog.Builder(getActivity())
                         .setIcon(R.drawable.ic_launcher)
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 66ec3af0..dcffa1fa 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -17,6 +17,9 @@
     <string name="send">Send</string>
 
     <!-- startup dialogs -->
+    <string name="startup_battery_optimization">Battery Optimization</string>
+    <string name="startup_battery_optimization_message">Android may disable/reduce DAVdroid synchronization after a few days. To prevent this, turn off battery optimization.</string>
+    <string name="startup_battery_optimization_disable">Turn off for DAVdroid</string>
     <string name="startup_dont_show_again">Don\'t show again</string>
     <string name="startup_development_version">DAVdroid Preview Release</string>
     <string name="startup_development_version_message">This is a development version of DAVdroid. Be aware that things may not work as expected. Please give us constructive feedback to improve DAVdroid.</string>