Voltage test says 12.6V (perfect). Load test reveals 8.2V under load (dead battery). The ₹500 jump-start becomes ₹8,000 battery replacement within a week.
Most sellers check voltage (₹300 multimeter), declare battery healthy. But voltage alone doesn’t reveal capacity loss, internal resistance, or sulfation. Load testing (the REAL test) requires specialized equipment and reveals the truth: that “healthy” battery fails under engine cranking load.
Why Voltage Test Isn’t Enough
Voltage test (engine off):
- 12.6V+: Fully charged
- 12.4V: 75% charged
- 12.2V: 50% charged
- <12.0V: Discharged
But: A failing battery can show 12.6V when idle, yet drop to 8V under load (starter motor)
That’s why load testing is mandatory
Load Testing (The Truth Teller)
What it tests: Battery’s ability to deliver current under load
Procedure:
- Apply load = 50% of CCA rating for 15 seconds
- Measure voltage during load
- Good: Voltage >9.6V
- Weak: Voltage 8-9.6V (replace soon)
- Failed: Voltage <8V (replace immediately)
Equipment: Load tester (₹2,000-5,000) or professional testing (₹200-500)
Battery Age
Manufacturing date sticker (on top):
- Format varies: MM/YY or coded
- Lifespan: 3-5 years (Indian climate)
If >4 years old: Replacement needed soon (₹4,000-12,000)
CCA Rating
CCA (Cold Cranking Amps): Current battery can deliver at 0°C for 30 seconds
Check: Rating on battery label (e.g., 500 CCA)
Higher CCA = better (especially for diesel engines)
If aftermarket battery:
- Is CCA rating equal to or higher than OEM?
- Lower CCA: May struggle to start engine (especially when cold)
Corrosion and Terminals
Check for:
- White/green powder on terminals (corrosion)
- Loose connections
Corrosion causes:
- Poor starting
- Alternator overworking (shortens alternator life)
Cleaning: ₹200-500
New terminals: ₹500-1,500
Alternator Charging Test
While engine running:
- Measure voltage at battery terminals
- Good: 13.8-14.4V
- Problem: <13.5V (alternator weak) or >14.8V (overcharging, voltage regulator fault)
Alternator failure cost: ₹8,000-25,000
Real Case
2019 Maruti Swift, 55,000 km
Seller: “Battery is fine, no issues”
Buyer’s voltage test: 12.5V (appeared healthy)
Buyer’s load test: 8.4V (failed)
Seller surprised: “But voltage was good!”
Explanation: Battery holds charge when idle but can’t deliver current under load
Negotiation: ₹6,000 discount (battery replacement cost)
Lesson: Load test reveals what voltage test hides
Conclusion
Voltage is surface-level. Load test is truth.
Protocol:
- Check battery age (sticker)
- Voltage test (engine off: >12.4V)
- Load test (under load: >9.6V)
- Alternator test (engine running: 13.8-14.4V)
- Corrosion check
Decision:
- Battery <3 years, passes load test: Proceed
- Battery 3-4 years, passes load test: Negotiate ₹3,000-5,000
- Battery >4 years OR fails load test: Negotiate ₹6,000-10,000
Key Takeaways
✓ Load test mandatory (voltage test insufficient)
✓ Battery >4 years old = replace (₹4-12K depending on capacity)
✓ Load test: >9.6V good, <8V failed (15-second test under 50% CCA load)
✓ Alternator: 13.8-14.4V when running (<13.5V = weak alternator, ₹8-25K replacement)
✓ CCA rating matters (diesel needs higher CCA than petrol)
Related: Electrical System Checks
Professional battery + alternator diagnostics
Voltage lies. Load test tells truth. Test before you trust.