diff --git a/app.py b/app.py
index 29c745f..81082a3 100644
--- a/app.py
+++ b/app.py
@@ -1139,7 +1139,15 @@ def create_app(config_object="config"):
             return redirect(url_for("device_detail", device_id=device_id))
         increment = 1 if request.form.get("increment_cycles") else 0
         notes = request.form.get("notes", "").strip() or None
-        installed = [b for b in device.batteries if b.status == "installed"]
+        if device.has_children():
+            installed = [
+                b
+                for child in device.children
+                for b in child.batteries
+                if b.status == "installed"
+            ]
+        else:
+            installed = [b for b in device.batteries if b.status == "installed"]
         if not installed:
             flash("No installed batteries to log.", "warning")
             return redirect(url_for("device_detail", device_id=device_id))
diff --git a/templates/device_detail.html b/templates/device_detail.html
index 57a9969..1975d32 100644
--- a/templates/device_detail.html
+++ b/templates/device_detail.html
@@ -232,6 +232,32 @@
 </div>
 {% endif %}
 
+{% if device.has_children() and flat_installed %}
+<div class="card">
+  <h2>Charge All Installed Batteries</h2>
+  <form method="post" action="{{ url_for('device_charge_all', device_id=device.id) }}"
+        style="display:flex;gap:0.5rem;flex-wrap:wrap;align-items:flex-end;">
+    <div class="form-group" style="margin:0;flex:1;min-width:140px;">
+      <label>Date</label>
+      <input type="date" name="charged_date" required>
+    </div>
+    <div class="form-group" style="margin:0;align-self:flex-end;padding-bottom:1rem;">
+      <label style="display:flex;align-items:center;gap:0.4rem;font-weight:normal;cursor:pointer;">
+        <input type="checkbox" name="increment_cycles" value="1" checked>
+        Increment charge cycles
+      </label>
+    </div>
+    <div class="form-group" style="margin:0;flex:2;min-width:160px;">
+      <label>Notes (optional)</label>
+      <input type="text" name="notes" placeholder="e.g. overnight charge">
+    </div>
+    <div style="padding-bottom:1rem;">
+      <button class="btn btn-primary" type="submit">Log Charge for All</button>
+    </div>
+  </form>
+</div>
+{% endif %}
+
 {% if not device.has_children() %}
 <div class="card">
   <h2>Install Batteries</h2>
diff --git a/tests/test_acceptance.py b/tests/test_acceptance.py
index 5f8d82d..2455cc0 100644
--- a/tests/test_acceptance.py
+++ b/tests/test_acceptance.py
@@ -1066,5 +1066,32 @@ def test_parent_battery_summary_flat(client):
     # Both child names linked in the component column
     assert b"Sensor A" in resp.data
     assert b"Sensor B" in resp.data
-    # Only one "Installed Batteries" heading
-    assert resp.data.count(b"Installed Batteries") == 1
+    # Flat table heading appears once (not duplicated per sub-component)
+    assert resp.data.count(b"<h2>Installed Batteries</h2>") == 1
+
+
+def test_device_charge_all_parent(client):
+    _setup_parent_with_two_children(client)
+    client.post("/battery/add", data={"brand": "Eneloop", "label": "E001", "size": "AA"})
+    client.post("/battery/add", data={"brand": "Eneloop", "label": "E002", "size": "AA"})
+    client.post("/device/2/install-one", data={"battery_id": "1"})
+    client.post("/device/3/install-one", data={"battery_id": "2"})
+    resp = client.post(
+        "/device/1/charge-all",
+        data={"charged_date": "2025-06-01", "increment_cycles": "1"},
+        follow_redirects=True,
+    )
+    assert resp.status_code == 200
+    assert b"Logged charge for 2 batteri" in resp.data
+    assert b"+cycles" in resp.data
+
+
+def test_device_charge_all_parent_no_installed(client):
+    _setup_parent_with_two_children(client)
+    resp = client.post(
+        "/device/1/charge-all",
+        data={"charged_date": "2025-06-01"},
+        follow_redirects=True,
+    )
+    assert resp.status_code == 200
+    assert b"No installed batteries" in resp.data