Track battery percentage history; skip poll write when value unchanged

templates/battery_detail.html

@@ -220,6 +220,37 @@
   </form>
 </div>
 
+<!-- Percentage History -->
+<div class="card">
+  <h2>Percentage History</h2>
+  {% if pct_logs %}
+  <div class="table-wrap">
+    <table class="responsive-table">
+      <thead>
+        <tr><th>Date / Time</th><th>%</th><th>Source</th></tr>
+      </thead>
+      <tbody>
+        {% for entry in pct_logs %}
+        <tr>
+          <td data-label="Date / Time">{{ entry.recorded_at }}</td>
+          <td data-label="%">
+            {% if entry.percentage < 20 %}
+              <span class="badge badge-warning">⚠ {{ entry.percentage }}%</span>
+            {% else %}
+              {{ entry.percentage }}%
+            {% endif %}
+          </td>
+          <td data-label="Source" class="text-muted">{{ entry.source or '—' }}</td>
+        </tr>
+        {% endfor %}
+      </tbody>
+    </table>
+  </div>
+  {% else %}
+  <p class="text-muted" style="margin-bottom:0;">No percentage history yet.</p>
+  {% endif %}
+</div>
+
 <!-- Edit Details -->
 <div class="card">
   <h2>Edit Details</h2>