diff --git a/apps/powermanager/ChangeLog b/apps/powermanager/ChangeLog
index f0b60a45a..a83e8c676 100644
--- a/apps/powermanager/ChangeLog
+++ b/apps/powermanager/ChangeLog
@@ -1,3 +1,5 @@
 0.01: New App!
 0.02: Allow forcing monotonic battery voltage/percentage
 0.03: Use default Bangle formatter for booleans
+0.04: Remove calibration with current voltage (Calibrate->Auto) as it is now handled by settings app
+      Allow automatic calibration on every charge longer than 3 hours
diff --git a/apps/powermanager/README.md b/apps/powermanager/README.md
index 434ec814e..88b3c370a 100644
--- a/apps/powermanager/README.md
+++ b/apps/powermanager/README.md
@@ -3,8 +3,9 @@
 Manages settings for charging.
 Features:
 * Warning threshold to be able to disconnect the charger at a given percentage
-* Set the battery calibration offset.
+* Set the battery calibration offset
 * Force monotonic battery percentage or voltage
+* Automatic calibration on charging uninterrupted longer than 3 hours (reloads of the watch reset the timer).
 
 ## Internals
 
diff --git a/apps/powermanager/boot.js b/apps/powermanager/boot.js
index 077e24413..3ddaad8e0 100644
--- a/apps/powermanager/boot.js
+++ b/apps/powermanager/boot.js
@@ -48,4 +48,13 @@
       return v;
     };
   }
+  
+  if (settings.autoCalibration){
+    let chargeStart;
+    Bangle.on("charging", (charging)=>{
+      if (charging) chargeStart = Date.now();
+      if (chargeStart && !charging && (Date.now() - chargeStart > 1000*60*60*3)) require("powermanager").setCalibration();
+      if (!charging) chargeStart = undefined;
+    });
+  }
 })();
diff --git a/apps/powermanager/lib.js b/apps/powermanager/lib.js
new file mode 100644
index 000000000..f4a7e3378
--- /dev/null
+++ b/apps/powermanager/lib.js
@@ -0,0 +1,6 @@
+// set battery calibration value by either applying the given value or setting the currently read battery voltage
+exports.setCalibration = function(calibration){
+  let s = require('Storage').readJSON("setting.json", true) || {};
+  s.batFullVoltage = calibration?calibration:((analogRead(D3) + analogRead(D3) + analogRead(D3) + analogRead(D3)) / 4);
+  require('Storage').writeJSON("setting.json", s);
+}
diff --git a/apps/powermanager/metadata.json b/apps/powermanager/metadata.json
index dd1727657..0777feee3 100644
--- a/apps/powermanager/metadata.json
+++ b/apps/powermanager/metadata.json
@@ -2,7 +2,7 @@
   "id": "powermanager",
   "name": "Power Manager",
   "shortName": "Power Manager",
-  "version": "0.03",
+  "version": "0.04",
   "description": "Allow configuration of warnings and thresholds for battery charging and display.",
   "icon": "app.png",
   "type": "bootloader",
@@ -12,6 +12,7 @@
   "storage": [
     {"name":"powermanager.boot.js","url":"boot.js"},
     {"name":"powermanager.settings.js","url":"settings.js"},
+    {"name":"powermanager","url":"lib.js"},
     {"name":"powermanager.default.json","url":"default.json"}
   ]
 }
diff --git a/apps/powermanager/settings.js b/apps/powermanager/settings.js
index 7cc683024..9eeb29e00 100644
--- a/apps/powermanager/settings.js
+++ b/apps/powermanager/settings.js
@@ -23,7 +23,6 @@
     '': {
       'title': 'Power Manager'
     },
-    '< Back': back,
     'Monotonic percentage': {
       value: !!settings.forceMonoPercentage,
       onchange: v => {
@@ -44,29 +43,29 @@
     }
   };
 
-
   function roundToDigits(number, stepsize) {
     return Math.round(number / stepsize) * stepsize;
   }
 
-  function getCurrentVoltageDirect() {
-    return (analogRead(D3) + analogRead(D3) + analogRead(D3) + analogRead(D3)) / 4;
-  }
-
   var stepsize = 0.0002;
-  var full = 0.32;
+  var full = 0.3144;
 
   function getInitialCalibrationOffset() {
     return roundToDigits(systemsettings.batFullVoltage - full, stepsize) || 0;
   }
 
-
   var submenu_calibrate = {
     '': {
-      title: "Calibrate"
+      title: "Calibrate",
+      back: function() {
+        E.showMenu(mainmenu);
+      },
     },
-    '< Back': function() {
-      E.showMenu(mainmenu);
+    'Autodetect': {
+      value: !!settings.autoCalibration,
+      onchange: v => {
+        writeSettings("autoCalibration", v);
+      }
     },
     'Offset': {
       min: -0.05,
@@ -75,25 +74,9 @@
       value: getInitialCalibrationOffset(),
       format: v => roundToDigits(v, stepsize).toFixed((""+stepsize).length - 2),
       onchange: v => {
-        print(typeof v);
-        systemsettings.batFullVoltage = v + full;
-        require("Storage").writeJSON("setting.json", systemsettings);
+        require("powermanager").setCalibration(v + full);
       }
     },
-    'Auto': function() {
-      var newVoltage = getCurrentVoltageDirect();
-      E.showAlert("Please charge fully before auto setting").then(() => {
-        E.showPrompt("Set current charge as full").then((r) => {
-          if (r) {
-            systemsettings.batFullVoltage = newVoltage;
-            require("Storage").writeJSON("setting.json", systemsettings);
-            //reset value shown in menu to the newly set one
-            submenu_calibrate.Offset.value = getInitialCalibrationOffset();
-            E.showMenu(mainmenu);
-          }
-        });
-      });
-    },
     'Clear': function() {
       E.showPrompt("Clear charging offset?").then((r) => {
         if (r) {
@@ -109,10 +92,10 @@
 
   var submenu_chargewarn = {
     '': {
-      title: "Charge warning"
-    },
-    '< Back': function() {
-      E.showMenu(mainmenu);
+      title: "Charge warning",
+      back: function() {
+        E.showMenu(mainmenu);
+      },
     },
     'Enabled': {
       value: !!settings.warnEnabled,