🔋 EV Battery Health Calculator

The Degradation Math (Worked for a 3-Year-Old EV)

Here is the exact computation the calculator runs, using the default inputs (3 years old, 45,000 km, moderate climate, rarely fast-charged):

1. Age degradation: 3 years × 2.0%/year = 6.0%
2. Mileage degradation: 45,000 km ÷ 10,000 × 0.8% = 3.6%
3. Base degradation: 6.0% + 3.6% = 9.6%
4. Climate factor: Moderate (20-30°C) = 1.0 (no penalty)
5. Fast charging factor: Rarely = 1.0 (no penalty)
6. Total degradation: 9.6% × 1.0 × 1.0 = 9.6%
7. Battery health: 100% − 9.6% = 90.4%

Base degradation rate of 2% per year is an average of LFP (1.5-2.5%/yr) and NMC (2-3%/yr) chemistries. Mileage degradation of 0.8% per 10,000 km reflects typical Indian driving conditions. Hot climate (35°C+) adds a 15% penalty; frequent DC fast charging adds a 10% penalty. The model caps degradation at 40% (60% minimum health) — below this, battery replacement is typically needed.

Degradation Table: Year-by-Year Battery Health

How battery health declines over time under different conditions. All assume 15,000 km/year driving:

The 5-year row is highlighted because most EV warranties cover 8 years / 160,000 km. At 5 years with moderate conditions, your battery retains 84% — still well above the 70% warranty threshold. Hot climate + frequent fast charging pushes 8-year health to 67.8%, just below the warranty floor.

LFP vs NMC: Why Battery Chemistry Matters

Most Indian EVs use one of two battery chemistries, and they degrade at different rates:

LFP batteries handle Indian heat better (higher thermal stability) and typically last longer, but have lower energy density (shorter range per kg). NMC batteries offer more range but degrade slightly faster and are more sensitive to high temperatures. If you live in a hot climate (Rajasthan, Gujarat, Tamil Nadu summers), LFP is the safer long-term choice.

What the Warranty Actually Covers

Most Indian EV manufacturers offer an 8-year / 160,000 km battery warranty. But read the fine print: the warranty typically covers manufacturing defects and sudden failure, not gradual capacity loss. Some manufacturers specify a threshold (usually 70% capacity retention) below which they'll replace the battery — but only if the degradation isn't caused by "improper use" (which can include frequent fast charging or deep discharging, depending on the OEM's terms).

Check your warranty document for the exact capacity threshold and exclusions before relying on warranty coverage for degradation.

The Common Mistake: Charging to 100% Every Day

Holding a battery at 100% state of charge stresses the cells and accelerates degradation. For daily city driving, charge to 80% and discharge to 20% — this "80-20 window" minimises cell stress and can extend battery life by 15-20%. Reserve 100% charges for highway trips when you need the full range. Most EVs let you set a daily charge limit in the infotainment system or companion app.

Edge Case: Infrequent Use Causes Degradation Too

Batteries degrade even when not driven — calendar aging. If you leave your EV parked for weeks at 100% charge in hot weather, the battery degrades faster than if you'd been driving it daily at moderate charge levels. If you're storing an EV for more than a month: charge to 50-60% (not 100%), park in shade or a covered space, and check the charge level monthly. The 50% storage level minimises cell stress.

Decision Framework: When to Replace the Battery

• Health above 85%: No action needed. Battery performs close to new. Range reduction is barely noticeable.
• Health 75-85%: Noticeable range reduction (10-20% less than new). Plan charging more carefully on long trips. Not yet replacement-worthy.
• Health 70-75%: Check your warranty — if it covers capacity below 70%, you may be approaching a free replacement. If not, budget ₹3-6 lakh for a replacement pack (varies by model).
• Health below 70%: Consider replacement. Range is 30%+ below new, which may not meet your daily needs. Check warranty coverage first.
• Health below 60%: Replacement is necessary for practical use. The calculator caps at 60% because below this, the battery's usable capacity is too low for reliable daily driving.

The 2-Minute Self-Check

1. Enter your EV's age (years since purchase) and total odometer reading.
2. Set the climate to match where you drive most (hot if summer temps regularly exceed 35°C).
3. Set fast charging usage honestly — if you use DC fast chargers more than 30% of the time, select "Often".
4. Check the estimated health. Compare it to what your car's app or dash display shows (if available).
5. If health is below 80%, start planning: check your warranty terms and research replacement pack costs.

Your Next Steps

1. Run the calculator with your EV's actual age and mileage.
2. If health is declining faster than expected, reduce DC fast charging and set a daily charge limit of 80%.
3. Check your real-world range at the Range Estimator — degradation reduces range proportionally.
4. See charging costs at the Charging Cost Calculator.
5. Compare overall running costs vs petrol at the EV vs Petrol Calculator.

Editor Note

Reviewed June 2026. Degradation rates are statistical averages based on LFP and NMC battery chemistry research. Individual battery health varies with charging habits, climate, and usage. The calculator caps at 60% minimum health - below this, replacement is typically needed. If you spot an outdated figure, please contact us.