diff --git a/frontend/src/components/StatusBar.tsx b/frontend/src/components/StatusBar.tsx
index ee55c98..eb97f3f 100644
--- a/frontend/src/components/StatusBar.tsx
+++ b/frontend/src/components/StatusBar.tsx
@@ -17,36 +17,10 @@ import {
   BATTERY_DISPLAY_CHANGE_EVENT,
   getShowBatteryPercent,
   getShowBatteryVoltage,
+  mvToPercent,
 } from '../utils/batteryDisplay';
 import { cn } from '@/lib/utils';
 
-// Meshtastic default OCV table (meshtastic/firmware src/power.h)
-const OCV_TABLE: [number, number][] = [
-  [4190, 100],
-  [4050, 90],
-  [3990, 80],
-  [3890, 70],
-  [3800, 60],
-  [3720, 50],
-  [3630, 40],
-  [3530, 30],
-  [3420, 20],
-  [3300, 10],
-  [3100, 0],
-];
-
-function mvToPercent(mv: number): number {
-  if (mv >= OCV_TABLE[0][0]) return 100;
-  if (mv <= OCV_TABLE[OCV_TABLE.length - 1][0]) return 0;
-  for (let i = 0; i < OCV_TABLE.length - 1; i++) {
-    const [highMv, highPct] = OCV_TABLE[i];
-    const [lowMv, lowPct] = OCV_TABLE[i + 1];
-    if (mv >= lowMv)
-      return Math.round(lowPct + ((mv - lowMv) / (highMv - lowMv)) * (highPct - lowPct));
-  }
-  return 0;
-}
-
 interface StatusBarProps {
   health: HealthStatus | null;
   config: RadioConfig | null;
diff --git a/frontend/src/test/batteryDisplay.test.ts b/frontend/src/test/batteryDisplay.test.ts
new file mode 100644
index 0000000..c79eca6
--- /dev/null
+++ b/frontend/src/test/batteryDisplay.test.ts
@@ -0,0 +1,44 @@
+import { describe, expect, it } from 'vitest';
+import { mvToPercent, formatBatteryLabel } from '../utils/batteryDisplay';
+
+describe('mvToPercent', () => {
+  it('clamps to 100 above table ceiling', () => {
+    expect(mvToPercent(4500)).toBe(100);
+    expect(mvToPercent(4190)).toBe(100);
+  });
+
+  it('clamps to 0 below table floor', () => {
+    expect(mvToPercent(3100)).toBe(0);
+    expect(mvToPercent(2800)).toBe(0);
+  });
+
+  it('returns exact table values at boundaries', () => {
+    expect(mvToPercent(4050)).toBe(90);
+    expect(mvToPercent(3630)).toBe(40);
+  });
+
+  it('interpolates between table entries', () => {
+    // Midpoint between 3630 (40%) and 3720 (50%) = 3675 → ~45%
+    const mid = mvToPercent(3675);
+    expect(mid).toBeGreaterThan(40);
+    expect(mid).toBeLessThan(50);
+  });
+});
+
+describe('formatBatteryLabel', () => {
+  it('returns null when both toggles are off', () => {
+    expect(formatBatteryLabel(4050, false, false)).toBeNull();
+  });
+
+  it('returns percentage only', () => {
+    expect(formatBatteryLabel(4050, true, false)).toBe('90%');
+  });
+
+  it('returns voltage only', () => {
+    expect(formatBatteryLabel(4050, false, true)).toBe('4050mV');
+  });
+
+  it('returns combined when both enabled', () => {
+    expect(formatBatteryLabel(4050, true, true)).toBe('90% (4050mV)');
+  });
+});
diff --git a/frontend/src/utils/batteryDisplay.ts b/frontend/src/utils/batteryDisplay.ts
index 3617bf0..a5c12ec 100644
--- a/frontend/src/utils/batteryDisplay.ts
+++ b/frontend/src/utils/batteryDisplay.ts
@@ -1,5 +1,44 @@
 export const BATTERY_DISPLAY_CHANGE_EVENT = 'remoteterm-battery-display-change';
 
+// Meshtastic default OCV table (meshtastic/firmware src/power.h)
+const OCV_TABLE: [number, number][] = [
+  [4190, 100],
+  [4050, 90],
+  [3990, 80],
+  [3890, 70],
+  [3800, 60],
+  [3720, 50],
+  [3630, 40],
+  [3530, 30],
+  [3420, 20],
+  [3300, 10],
+  [3100, 0],
+];
+
+export function mvToPercent(mv: number): number {
+  if (mv >= OCV_TABLE[0][0]) return 100;
+  if (mv <= OCV_TABLE[OCV_TABLE.length - 1][0]) return 0;
+  for (let i = 0; i < OCV_TABLE.length - 1; i++) {
+    const [highMv, highPct] = OCV_TABLE[i];
+    const [lowMv, lowPct] = OCV_TABLE[i + 1];
+    if (mv >= lowMv)
+      return Math.round(lowPct + ((mv - lowMv) / (highMv - lowMv)) * (highPct - lowPct));
+  }
+  return 0;
+}
+
+export function formatBatteryLabel(
+  mv: number,
+  showPercent: boolean,
+  showVoltage: boolean
+): string | null {
+  if (!showPercent && !showVoltage) return null;
+  const pct = mvToPercent(mv);
+  if (showPercent && showVoltage) return `${pct}% (${mv}mV)`;
+  if (showPercent) return `${pct}%`;
+  return `${mv}mV`;
+}
+
 const PERCENT_KEY = 'remoteterm-show-battery-percent';
 const VOLTAGE_KEY = 'remoteterm-show-battery-voltage';