MG Comet & Windsor EV Battery Problems: Repair & Cost

The battery is the single most expensive part of any electric car, and on the MG Comet EV and MG Windsor EV it is also the part owners worry about most. The Comet runs a compact 17.3 kWh pack built for short city hops, while the Windsor uses a larger 38 kWh pack (and a 52.9 kWh pack on the Windsor Pro) aimed at families and longer commutes. Both are lithium-ion prismatic packs, and MG markets them aggressively on warranty — including a headline "lifetime battery warranty" for the first owner.

That warranty is reassuring, but it does not stop the everyday questions. Why did the range suddenly drop? Why does the battery seem to fall from 100% to 80% within the first few kilometres? Is a single dead cell going to cost a fortune to fix? And with the Windsor offered on a Battery-as-a-Service (BaaS) rental plan, who is even responsible for the pack — you or MG?

This guide answers all of that in plain language for Indian owners. We cover the real battery specs, the genuine warranty terms (years, kilometres and the fine print), the most common owner-reported battery complaints, what actually causes them in Indian conditions, how to check your battery's State of Health (SoH), and realistic, indicative repair-versus-replacement costs in rupees. We also draw a clear line between the checks you can safely do yourself and the high-voltage work that must always go to a trained technician.

The Comet and Windsor batteries at a glance

Before troubleshooting, it helps to know exactly what is sitting under your car.

• MG Comet EV uses a 17.3 kWh lithium-ion prismatic pack with an ARAI-claimed range of around 230 km. Real-world city range is typically lower, in the 120–170 km band depending on AC use, traffic and driving style. The pack is IP67-rated for dust and water resistance.
• MG Windsor EV uses a 38 kWh LFP (lithium iron phosphate) prismatic pack with a claimed range of around 331 km. The Windsor Pro steps up to a 52.9 kWh pack with a claimed range of around 449 km.
• The Comet charges via a 3.3 kW or 7.4 kW AC charger (roughly 7 hours and 3.5 hours for a full charge respectively). The Comet does not support DC fast charging.
• The Windsor supports DC fast charging up to ~60 kW, taking roughly 45–50 minutes for a 20–80% top-up, and around 9.5 hours on a 7.4 kW home AC charger.

Both packs use prismatic cells. The Windsor's chemistry is LFP, which is inherently more thermally stable and tends to degrade more gradually than nickel-rich NMC chemistry. The Comet is widely reported as a prismatic LFP-type lithium-ion pack as well, though MG's spec sheets simply list it as "lithium-ion." Either way, the failure modes and the way you diagnose them are broadly similar.

Common MG Comet and Windsor battery problems

Most "battery" complaints fall into a handful of buckets. Knowing which bucket you are in is the first step to a fix.

Range loss and faster-than-expected depletion

This is by far the most common complaint, especially on the Comet. Some owners report that on the basic 3.3 kW charger, the indicated charge appears to fall quickly in the first stretch of city driving — in a few reported cases owners say they saw a sizeable drop (around 20%) within the first 50 km of stop-go traffic with the AC running. On a small 17.3 kWh pack, every kilometre of range matters, so this feels dramatic even when the underlying battery is healthy.

Range loss comes in two flavours. Temporary range loss is caused by heat, AC load, aggressive driving or a cold/very hot pack, and it returns to normal when conditions change. Permanent range loss is genuine capacity degradation — the pack physically holds less energy than when new. Distinguishing the two is the heart of any good diagnosis.

Gradual capacity degradation

All lithium batteries lose a little capacity every year. For LFP packs in Indian conditions, a healthy ageing curve is roughly 2–3% per year in the early years, slowing thereafter. A loss of more than that — or a sudden step-down — points to a problem worth investigating. Some independent checks on early Comets reported usable range falling on certain cars after relatively low mileage, which is usually a sign of cell imbalance rather than the whole pack wearing out.

Battery "won't hold charge" or drops fast at rest

If your Comet or Windsor loses a meaningful chunk of charge while simply parked overnight, that is not normal LFP behaviour. Causes include a parasitic 12V system drain, a faulty cell that self-discharges quickly, or a BMS that is mis-reading the true state of charge. This symptom deserves a professional check because a single weak cell can drag down the entire pack.

BMS errors and warning lights

The Battery Management System is the brain of the pack. A turtle-mode warning, a battery fault icon, reduced power, or a sudden drop in available charge can all be BMS-triggered. Sometimes the BMS is correctly protecting a genuinely faulty pack; sometimes it has simply lost calibration and is reporting numbers that no longer match reality. A diagnostic scan tells you which.

Cell imbalance

In a pack, cells should stay within a few millivolts of each other. When one or more cells drift, the BMS limits the whole pack to protect the weakest cell — so you lose range even though most of the pack is fine. Cell imbalance has been flagged as a real-world issue on some early Comets and is one of the most fixable battery faults, because it can often be addressed without replacing the entire pack.

Heating, swelling or charging-linked symptoms

Excessive heat at the pack, a swollen-feeling floor, a strong chemical smell, or charging that repeatedly cuts out are all serious. These are rare, but they must never be ignored or driven through. Treat any suspected swelling, smoke or burning smell as a fire-safety emergency, not a routine fault. Charging-linked symptoms (charging stops early, won't start, or throws an error) often turn out to be a charger, cable, socket or onboard-charger issue rather than the cells themselves — which is good news, because those are cheaper to fix.

What causes these battery problems

EV batteries rarely fail for one reason. In Indian conditions, a few factors stack up.

• Heat. Sustained ambient temperatures above 35°C accelerate lithium-ion ageing, and large parts of India see that for months at a stretch. LFP tolerates heat better than NMC, but no chemistry is immune. Cars parked in the open all day in peak summer, then charged immediately while still hot, age faster.
• DC fast-charging habits (Windsor). Repeated back-to-back DC fast charges generate more heat and stress than slow AC charging. The occasional highway fast-charge is fine; making it your only charging method will shorten pack life over the years. The Comet sidesteps this because it is AC-only.
• State-of-charge habits. Sitting at 100% in the heat, or routinely running down to near 0%, is hard on the pack. For LFP, the practical sweet spot for daily use is roughly a 20–80% window, with an occasional full charge to let the BMS recalibrate.
• Cell imbalance and ageing. Manufacturing tolerances mean cells age at slightly different rates. Over time, and accelerated by heat and deep cycling, that drift becomes measurable range loss.
• BMS faults and calibration drift. The BMS estimates capacity and balances cells. Faulty sensors, outdated firmware or lost calibration can produce range numbers that look like battery failure but are really a software or sensor problem.
• 12V battery and electrical gremlins. A weak conventional 12V battery can cause no-start, false warnings and odd BMS behaviour that owners often mistake for a main-pack fault.

How to check your battery's State of Health (SoH)

State of Health is the headline number: how much capacity your pack retains versus when it was new. A pack at 100% SoH is as-new; at 80% it has lost a fifth of its usable capacity. Here is how to assess it, from easy to definitive.

Read the in-car and app data

Start with the MG iSMART app and the car's energy screens. Watch your average efficiency (km per kWh, or Wh/km) and your full-charge indicated range over several weeks. A slow, steady decline tracks normal ageing. A sudden drop, or a full-charge range far below what you used to get in the same season and driving pattern, is a red flag.

Run a controlled range test

The most honest DIY test is a real-world capacity check.

1. Charge to 100% in moderate weather (not a 44°C afternoon).
2. Note the odometer and the indicated range.
3. Drive a normal, repeatable city/highway mix with consistent AC use.
4. Track how far you actually travel against how much charge you consume.

Compare the energy you used for the distance covered with the pack's rated kWh. Repeat the test a couple of times to average out traffic and weather. This won't give a lab-grade SoH percentage, but it reliably separates "my range feels low" from "my range genuinely is low."

Get a professional SoH diagnosis

For a real number you need a proper read of the pack via the car's diagnostic port. A technician can pull per-cell voltages, pack temperature, charge/discharge history and the BMS's own capacity estimate, then calculate SoH and flag any imbalanced or weak cells. Get a professional diagnosis when: your range has dropped sharply, you see battery or turtle warnings, the car won't hold charge overnight, you are about to buy or sell a used Comet/Windsor, or you simply want a documented baseline. You can book a battery health check with ev.care to get this done independently and have the readings explained in plain language.

MG Comet and Windsor battery warranty — what's actually covered

MG's battery warranty is genuinely strong, but the details matter.

• Standard battery warranty on the Comet and Windsor is 8 years or 1,20,000–1,60,000 km depending on the car and policy. The Comet's pack is commonly listed at 8 years / 1.2 lakh km.
• Lifetime battery warranty (first owner). MG offers an unlimited-kilometre lifetime warranty on the battery pack to the first owner on these models. It covers manufacturing defects and malfunction of the pack.
• Resale roll-back. This is the crucial fine print: the lifetime cover is tied to the first owner. When the car is sold, the battery warranty typically rolls back to 8 years or 1,60,000 km, whichever comes first. If you are buying a used Comet or Windsor, do not assume the lifetime cover transfers — confirm the remaining warranty in writing.

A few important caveats apply to any EV battery warranty:

• Capacity-retention clauses. OEM battery warranties generally cover the pack falling below a defined capacity threshold (commonly in the region of around 70% SoH) within the warranty period, in addition to outright failure. Gradual, normal degradation above that threshold is usually considered wear and tear, not a defect. Always read your specific warranty booklet for the exact percentage and conditions, as terms can change by variant and model year.
• Accidental damage is not warranty. Physically damaging the pack (a hard underbody impact, flooding, etc.) is an insurance matter, not a warranty claim. This is exactly why a dedicated EV/battery cover on your motor insurance is worth having.
• Voiding risks. Unauthorised opening of the high-voltage pack, third-party "repairs" that aren't documented, or tampering can jeopardise the warranty. If your car is in warranty, route pack-level work through MG first.

Windsor BaaS — who owns the battery?

The Windsor is also sold under Battery-as-a-Service (BaaS), where you buy the car at a lower upfront price (battery excluded) and pay a monthly rental for the pack. Indicatively, the 38 kWh pack is charged at around ₹3.5 per km, with a minimum monthly outgo of roughly ₹5,250 (covering up to ~1,500 km), while the Pro's larger pack is priced higher per km (around ₹4.5 per km). Charging electricity is separate (MG pegs it at roughly ₹1 per km).

Under BaaS, the battery is owned by the BaaS provider/financier, not you — which means battery faults, degradation and replacement are the provider's responsibility for as long as you are on the plan. That removes the single biggest EV ownership risk from your shoulders, but you keep paying monthly regardless of how little you drive. If you bought the Windsor with the battery (outright, from around ₹13.5 lakh ex-showroom for the base variant), then the pack is yours and the warranty terms above apply.

How to claim a battery warranty

1. Document the symptom early — dates, photos of warning lights, your range logs.
2. Report it to an authorised MG service centre while in warranty; delays can complicate a claim.
3. Ask for a written SoH/diagnostic report. This is your evidence, especially for a capacity-retention claim.
4. If you want a second opinion before or after the dealer visit, an independent battery health check gives you leverage and clarity.

Repair vs replace — and indicative costs

The biggest myth in EV ownership is that a single battery problem means buying a whole new pack. Often it does not.

Module or cell-level repair

Many real-world battery faults — cell imbalance, one or two weak cells, a failed module, a BMS sensor or calibration issue — can be fixed without replacing the entire pack. A skilled EV battery workshop can open the pack under controlled conditions, identify the faulty module or cells, and replace or rebalance only that section. Indicative costs for module/cell-level work and BMS-related repairs typically run in the ₹15,000–₹90,000 range depending on how many cells/modules are involved and parts availability. A simple BMS recalibration or a cell-rebalancing session sits at the lower end; a full module swap sits higher.

Full pack replacement

A complete pack replacement is the worst case and the most expensive. As a yardstick, a Windsor's 38 kWh pack bought as part of the car accounts for a large share of the roughly ₹13.5 lakh outright price, so a full out-of-warranty replacement is a major expense — indicatively well into the multiple lakhs. The Comet's smaller 17.3 kWh pack would be proportionally less but still a significant sum. These are precisely the scenarios the warranty exists to cover, which is why protecting and documenting your warranty matters so much.

The practical takeaway: always get a proper diagnosis before agreeing to a full pack replacement. If a workshop or quote jumps straight to "replace the whole battery" without per-cell data showing widespread failure, get a second opinion. Many "dead" packs are revived with targeted module or BMS work at a fraction of the cost.

Safe DIY checks vs when to call a professional

High-voltage EV packs are dangerous. The Comet and Windsor packs operate at voltages that can injure or kill, and a damaged lithium pack can catch fire. Never open, probe or attempt to repair the high-voltage battery yourself. That work requires trained technicians, insulated tools, and proper safety procedures.

What you can safely do yourself:

• Track range, efficiency and full-charge range over time in the app and dashboard.
• Run the controlled range test described above.
• Keep the car's software updated and keep the 12V battery healthy.
• Charge in the 20–80% band for daily use and avoid leaving the car at 100% in extreme heat.
• Park in shade when possible and let a hot pack cool before charging.
• Inspect the charging cable, plug and home socket for damage or heat marks.

Call a professional immediately if you notice any of the following:

• A battery, turtle-mode or reduced-power warning that does not clear.
• A sharp, unexplained drop in range or charge that won't hold overnight.
• Any sign of swelling, a chemical or burning smell, smoke, or unusual heat from the floor or pack — in that case stop driving, park away from buildings and other vehicles, and call for help. Do not charge the car.
• Charging that repeatedly fails or cuts out.

If the symptom is charging-related rather than pack-related, our EV charging repair & service team can diagnose the charger, cable and onboard charging system, and you can run our free EV charging diagnostic tool first to narrow it down in a couple of minutes.

How ev.care helps with MG Comet and Windsor batteries

ev.care is an independent, brand-agnostic EV service network — we work on any EV, including the MG Comet and Windsor, alongside Tata, Ola, Ather, Hyundai and more. For battery concerns we offer:

• Full battery health checks with a documented SoH report you actually understand.
• BMS diagnostics to read per-cell voltages, temperatures and fault codes, and to tell genuine pack failure apart from a calibration or software issue.
• Cell- and module-level repair so you only replace what's actually faulty instead of an entire pack where that isn't warranted.
• Charging-system diagnosis and repair for the many "battery" complaints that turn out to be charger, cable or socket faults.
• An honest second opinion before you commit to an expensive pack replacement, and help understanding your warranty or BaaS coverage.

If your Comet or Windsor's range has dropped, the battery won't hold charge, or a warning light has appeared, the smartest first step is a proper diagnosis — book a battery health check and we'll tell you exactly what's going on.

For related reading, see our guides on Tata Nexon EV charging problems and diagnosing an EV that won't charge in India.

Frequently asked questions

Is the MG Comet or Windsor battery warranty really "lifetime"?

For the first owner, yes — MG offers an unlimited-kilometre lifetime warranty on the battery pack covering defects and malfunction. The catch is that it is tied to the first owner. When the car is sold, the battery warranty typically rolls back to 8 years or 1,60,000 km, whichever comes first. Always confirm the remaining cover in writing on a used car.

My MG Comet's range dropped suddenly — is the battery dead?

Probably not. Sudden range drops are most often caused by heat, heavy AC use, a low 12V battery, a BMS that has lost calibration, or cell imbalance — all of which are fixable. Genuine pack failure is far rarer. Run a controlled full-charge range test, and if range is truly low, get a professional SoH diagnosis before assuming the worst.

What's a normal rate of battery degradation for these LFP packs?

As a rough guide, healthy LFP packs in Indian conditions lose around 2–3% of capacity per year in the early years, slowing over time. Anything sharper than that, or a sudden step-down in usable range, is worth investigating. A documented SoH check gives you the real number rather than a guess.

Under the Windsor BaaS plan, who pays if the battery fails?

If you are on Battery-as-a-Service, the battery is owned by the BaaS provider/financier, so battery faults, degradation and replacement are their responsibility while you are on the plan — you keep paying the monthly rental (indicatively from about ₹5,250 a month for the 38 kWh pack). If you bought the Windsor with the battery outright, the pack is yours and MG's warranty terms apply.

How much does it cost to fix an MG EV battery in India?

It depends entirely on the fault. Cell rebalancing, BMS recalibration and single-module repairs are indicatively in the ₹15,000–₹90,000 range. A full pack replacement out of warranty runs into lakhs and is the worst case — which is exactly why you should get a proper diagnosis first, since many problems are fixable at module or cell level. In-warranty defects and capacity-retention claims should cost you nothing if covered.

Should I use DC fast charging on my Windsor every time?

No. Occasional DC fast charging on the road is perfectly fine, but making it your only charging method generates extra heat and accelerates ageing over the years. For daily use, slow AC charging in roughly the 20–80% window is gentler on the pack and will keep your SoH higher for longer.