diff --git a/app.py b/app.py
index 016b3b8..26a0250 100644
--- a/app.py
+++ b/app.py
@@ -2,7 +2,7 @@ from flask import Flask, render_template, redirect, url_for, request, flash, abo
 from sqlalchemy import create_engine, func
 from sqlalchemy.orm import scoped_session, sessionmaker
 
-from models import Base, Battery, Device
+from models import Base, Battery, Device, CapacityTest
 
 
 def create_app(config_object="config"):
@@ -105,8 +105,13 @@ def create_app(config_object="config"):
             .filter(Battery.storage_location.isnot(None))
             .distinct().order_by(Battery.storage_location).all()
         ]
+        capacity_tests = (db.query(CapacityTest)
+                          .filter_by(battery_id=battery_id)
+                          .order_by(CapacityTest.tested_date, CapacityTest.id)
+                          .all())
         return render_template("battery_detail.html", battery=battery,
-                               storage_locations=storage_locations)
+                               storage_locations=storage_locations,
+                               capacity_tests=capacity_tests)
 
     # ------------------------------------------------------------------ #
     # Battery — edit notes
@@ -130,8 +135,6 @@ def create_app(config_object="config"):
         battery.size                = f.get("size", "").strip() or None
         battery.chemistry           = f.get("chemistry", "").strip() or None
         battery.capacity_mah        = _int("capacity_mah")
-        battery.tested_capacity_mah = _int("tested_capacity_mah")
-        battery.tested_date         = f.get("tested_date", "").strip() or None
         battery.charge_cycles       = _int("charge_cycles")
         battery.purchase_date       = f.get("purchase_date", "").strip() or None
         battery.storage_location    = f.get("storage_location", "").strip() or None
@@ -140,6 +143,57 @@ def create_app(config_object="config"):
         flash("Details updated.", "success")
         return redirect(url_for("battery_detail", battery_id=battery_id))
 
+    # ------------------------------------------------------------------ #
+    # Battery — capacity test history
+    # ------------------------------------------------------------------ #
+
+    def _sync_latest_test(battery):
+        latest = (db.query(CapacityTest)
+                  .filter_by(battery_id=battery.id)
+                  .order_by(CapacityTest.tested_date.desc(), CapacityTest.id.desc())
+                  .first())
+        battery.tested_capacity_mah = latest.tested_capacity_mah if latest else None
+        battery.tested_date = latest.tested_date if latest else None
+
+    @app.route("/battery/<int:battery_id>/capacity-test/add", methods=["POST"])
+    def battery_capacity_test_add(battery_id):
+        battery = db.get(Battery, battery_id)
+        if battery is None:
+            abort(404)
+        mah_raw  = request.form.get("tested_capacity_mah", "").strip()
+        date_val = request.form.get("tested_date", "").strip()
+        notes    = request.form.get("notes", "").strip() or None
+        if not mah_raw or not date_val:
+            flash("Capacity (mAh) and date are required.", "error")
+            return redirect(url_for("battery_detail", battery_id=battery_id))
+        try:
+            mah = int(mah_raw)
+            if mah <= 0:
+                raise ValueError
+        except ValueError:
+            flash("Capacity must be a positive integer.", "error")
+            return redirect(url_for("battery_detail", battery_id=battery_id))
+        db.add(CapacityTest(battery_id=battery_id, tested_capacity_mah=mah,
+                            tested_date=date_val, notes=notes))
+        db.flush()
+        _sync_latest_test(battery)
+        db.commit()
+        flash("Test record added.", "success")
+        return redirect(url_for("battery_detail", battery_id=battery_id))
+
+    @app.route("/battery/<int:battery_id>/capacity-test/<int:test_id>/delete", methods=["POST"])
+    def battery_capacity_test_delete(battery_id, test_id):
+        battery = db.get(Battery, battery_id)
+        test    = db.get(CapacityTest, test_id)
+        if battery is None or test is None or test.battery_id != battery_id:
+            abort(404)
+        db.delete(test)
+        db.flush()
+        _sync_latest_test(battery)
+        db.commit()
+        flash("Test record deleted.", "success")
+        return redirect(url_for("battery_detail", battery_id=battery_id))
+
     # ------------------------------------------------------------------ #
     # Battery — assign
     # ------------------------------------------------------------------ #
diff --git a/models.py b/models.py
index 76e0a97..6cd25fa 100644
--- a/models.py
+++ b/models.py
@@ -49,6 +49,11 @@ class Battery(Base):
     storage_location    = Column(String(100), nullable=True)   # where stored when not installed
 
     device = relationship("Device", back_populates="batteries")
+    capacity_tests = relationship(
+        "CapacityTest", back_populates="battery",
+        order_by="CapacityTest.tested_date",
+        cascade="all, delete-orphan",
+    )
 
     def is_available(self):
         return self.status == "available"
@@ -61,3 +66,18 @@ class Battery(Base):
 
     def __repr__(self):
         return f"<Battery {self.label}>"
+
+
+class CapacityTest(Base):
+    __tablename__ = "capacity_test"
+
+    id                  = Column(Integer, primary_key=True, autoincrement=True)
+    battery_id          = Column(Integer, ForeignKey("battery.id", ondelete="CASCADE"), nullable=False)
+    tested_capacity_mah = Column(Integer, nullable=False)
+    tested_date         = Column(String(10), nullable=False)  # YYYY-MM-DD
+    notes               = Column(Text, nullable=True)
+
+    battery = relationship("Battery", back_populates="capacity_tests")
+
+    def __repr__(self):
+        return f"<CapacityTest {self.battery_id} {self.tested_date} {self.tested_capacity_mah}mAh>"
diff --git a/templates/battery_detail.html b/templates/battery_detail.html
index 94dafc9..f4ef0b5 100644
--- a/templates/battery_detail.html
+++ b/templates/battery_detail.html
@@ -76,6 +76,78 @@
   </table>
 </div>
 
+<!-- Capacity History -->
+<div class="card">
+  <h2>Capacity History</h2>
+
+  {% if capacity_tests|length >= 2 %}
+  <canvas id="capacity-chart"
+          style="width:100%;max-width:500px;height:140px;display:block;margin-bottom:1rem;"
+          width="500" height="140"></canvas>
+  {% endif %}
+
+  {% if capacity_tests %}
+  <div class="table-wrap">
+    <table class="responsive-table">
+      <thead>
+        <tr>
+          <th>Date</th>
+          <th>Capacity</th>
+          {% if battery.capacity_mah %}<th>Health</th>{% endif %}
+          <th>Notes</th>
+          <th></th>
+        </tr>
+      </thead>
+      <tbody>
+        {% for t in capacity_tests|sort(attribute='tested_date', reverse=True) %}
+        <tr>
+          <td data-label="Date">{{ t.tested_date }}</td>
+          <td data-label="Capacity">{{ t.tested_capacity_mah }} mAh</td>
+          {% if battery.capacity_mah %}
+            {% set pct = (t.tested_capacity_mah / battery.capacity_mah * 100)|round|int %}
+            {% if pct >= 80 %}{% set hc = "health-good" %}
+            {% elif pct >= 60 %}{% set hc = "health-warn" %}
+            {% else %}{% set hc = "health-bad" %}{% endif %}
+            <td data-label="Health"><span class="{{ hc }}">{{ pct }}%</span></td>
+          {% endif %}
+          <td data-label="Notes" class="text-muted">{{ t.notes or '—' }}</td>
+          <td data-label="">
+            <form class="inline" method="post"
+                  action="{{ url_for('battery_capacity_test_delete', battery_id=battery.id, test_id=t.id) }}"
+                  onsubmit="return confirm('Delete this test record?')">
+              <button class="btn btn-sm btn-danger" type="submit">Delete</button>
+            </form>
+          </td>
+        </tr>
+        {% endfor %}
+      </tbody>
+    </table>
+  </div>
+  {% else %}
+  <p class="text-muted" style="margin-bottom:0.75rem;">No test records yet.</p>
+  {% endif %}
+
+  <h3 style="font-size:1rem;margin:1rem 0 0.5rem;color:var(--text-h2);">Add Test Record</h3>
+  <form method="post" action="{{ url_for('battery_capacity_test_add', battery_id=battery.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:120px;">
+      <label>Capacity (mAh)</label>
+      <input type="number" name="tested_capacity_mah" min="1" placeholder="e.g. 1850" required>
+    </div>
+    <div class="form-group" style="margin:0;flex:1;min-width:140px;">
+      <label>Date</label>
+      <input type="date" name="tested_date" required>
+    </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. after 50 cycles">
+    </div>
+    <div style="padding-bottom:1rem;">
+      <button class="btn btn-primary" type="submit">Add</button>
+    </div>
+  </form>
+</div>
+
 <!-- Edit Details -->
 <div class="card">
   <h2>Edit Details</h2>
@@ -123,18 +195,6 @@
                value="{{ battery.charge_cycles or '' }}" placeholder="e.g. 50">
       </div>
 
-      <div class="form-group">
-        <label for="tested_capacity_mah">Tested Capacity (mAh)</label>
-        <input type="number" id="tested_capacity_mah" name="tested_capacity_mah" min="0"
-               value="{{ battery.tested_capacity_mah or '' }}" placeholder="e.g. 1850">
-      </div>
-
-      <div class="form-group">
-        <label for="tested_date">Test Date</label>
-        <input type="date" id="tested_date" name="tested_date"
-               value="{{ battery.tested_date or '' }}">
-      </div>
-
       <div class="form-group">
         <label for="purchase_date">Purchase Date</label>
         <input type="date" id="purchase_date" name="purchase_date"
@@ -198,6 +258,68 @@
 <a class="text-muted" href="{{ url_for('dashboard') }}">&larr; Back to Dashboard</a>
 
 <script>
+(function() {
+  var canvas = document.getElementById('capacity-chart');
+  if (!canvas) return;
+  var tests  = {{ capacity_tests | map(attribute='tested_capacity_mah') | list | tojson }};
+  var labels = {{ capacity_tests | map(attribute='tested_date') | list | tojson }};
+  if (tests.length < 2) return;
+
+  var s = getComputedStyle(document.documentElement);
+  var lineColor = s.getPropertyValue('--link').trim()       || '#2563eb';
+  var textColor = s.getPropertyValue('--text-muted').trim() || '#6b7280';
+  var gridColor = s.getPropertyValue('--border').trim()     || '#e2e8f0';
+
+  var dpr = window.devicePixelRatio || 1;
+  var W = canvas.offsetWidth || 500, H = 140;
+  canvas.width  = W * dpr; canvas.height = H * dpr;
+  canvas.style.width = W + 'px'; canvas.style.height = H + 'px';
+
+  var ctx = canvas.getContext('2d');
+  ctx.scale(dpr, dpr);
+
+  var PAD = {top: 12, right: 16, bottom: 28, left: 52};
+  var cW = W - PAD.left - PAD.right;
+  var cH = H - PAD.top  - PAD.bottom;
+
+  var minV = Math.min.apply(null, tests), maxV = Math.max.apply(null, tests);
+  var pad = (maxV - minV || 100) * 0.1;
+  minV -= pad; maxV += pad;
+  var range = maxV - minV;
+
+  function xOf(i) { return PAD.left + (i / (tests.length - 1)) * cW; }
+  function yOf(v) { return PAD.top  + cH - ((v - minV) / range) * cH; }
+
+  // Horizontal grid lines
+  ctx.lineWidth = 0.5;
+  [0, 0.5, 1].forEach(function(t) {
+    var y = PAD.top + cH * (1 - t);
+    ctx.strokeStyle = gridColor;
+    ctx.beginPath(); ctx.moveTo(PAD.left, y); ctx.lineTo(PAD.left + cW, y); ctx.stroke();
+    ctx.fillStyle = textColor; ctx.font = '10px system-ui'; ctx.textAlign = 'right';
+    ctx.fillText(Math.round(minV + t * range) + '', PAD.left - 4, y + 3);
+  });
+
+  // Line
+  ctx.strokeStyle = lineColor; ctx.lineWidth = 2; ctx.lineJoin = 'round';
+  ctx.beginPath();
+  tests.forEach(function(v, i) {
+    i === 0 ? ctx.moveTo(xOf(i), yOf(v)) : ctx.lineTo(xOf(i), yOf(v));
+  });
+  ctx.stroke();
+
+  // Dots + date labels (first and last only)
+  tests.forEach(function(v, i) {
+    ctx.fillStyle = lineColor;
+    ctx.beginPath(); ctx.arc(xOf(i), yOf(v), 3, 0, Math.PI * 2); ctx.fill();
+    if (i === 0 || i === tests.length - 1) {
+      ctx.fillStyle = textColor; ctx.font = '9px system-ui';
+      ctx.textAlign = i === 0 ? 'left' : 'right';
+      ctx.fillText(labels[i], xOf(i), H - 4);
+    }
+  });
+}());
+
 function metaSelectChanged(sel, inputId) {
   var input = document.getElementById(inputId);
   if (sel.value === '__new__') {
diff --git a/tests/test_acceptance.py b/tests/test_acceptance.py
index 41f6017..42b43c5 100644
--- a/tests/test_acceptance.py
+++ b/tests/test_acceptance.py
@@ -480,6 +480,33 @@ def test_edit_device_type(client):
     assert b"Flashlight" in resp.data
 
 
+def test_add_capacity_test(client):
+    client.post("/battery/add", data={"brand": "Eneloop", "count": "1"})
+    resp = client.post("/battery/1/capacity-test/add",
+                       data={"tested_capacity_mah": "1900", "tested_date": "2026-01-01"},
+                       follow_redirects=True)
+    assert resp.status_code == 200
+    assert b"1900" in resp.data
+
+
+def test_capacity_test_syncs_battery(client):
+    """Adding a test updates battery.tested_capacity_mah."""
+    client.post("/battery/add", data={"brand": "Eneloop", "count": "1"})
+    client.post("/battery/1/capacity-test/add",
+                data={"tested_capacity_mah": "1800", "tested_date": "2026-01-01"})
+    resp = client.get("/battery/1")
+    assert b"1800" in resp.data
+
+
+def test_delete_capacity_test(client):
+    client.post("/battery/add", data={"brand": "Eneloop", "count": "1"})
+    client.post("/battery/1/capacity-test/add",
+                data={"tested_capacity_mah": "1900", "tested_date": "2026-01-01"})
+    resp = client.post("/battery/1/capacity-test/1/delete", follow_redirects=True)
+    assert resp.status_code == 200
+    assert b"No test records" in resp.data
+
+
 def test_add_install_delete_battery(client):
     client.post("/device/add", data={"name": "Gadget", "battery_slots": "1"})
     client.post("/battery/add", data={"brand": "AcmeBrand", "count": "1"})