Your EV battery's health is measured as State of Health (SoH) — its current usable capacity versus when new. Large real-world data is reassuring: a study of 22,700+ vehicles found packs degrade about 2.3% per year and still hold roughly 81.6% of capacity after eight years, well above the ~70% most warranties guarantee. To monitor it: check the SoH figure in your car's menus or a reputable app, watch for sudden range drops, and keep records. To maintain it: keep daily charge in a moderate band (around 20–80% for NMC; 100% is fine for LFP), avoid leaving the car at 0% or 100% for long spells, favour AC/home charging day-to-day, and let the car manage battery temperature.
Battery health at a glance
| Metric | What it means | Healthy target |
|---|---|---|
| State of Health (SoH) | Usable capacity vs new | Above ~90% in early years; 80%+ at 8 yrs |
| Annual degradation | Capacity lost per year | ~2.3% per year (fleet average) |
| Warranty floor | Capacity guaranteed by maker | Commonly 70–75% over 8 yrs / 100,000 mi |
| Biggest stressor | What ages packs fastest | Heat + frequent high-power DC charging |
What 'battery health' actually means
Battery health is usually expressed as State of Health (SoH): the pack's current usable energy capacity as a percentage of its original capacity. A car at 90% SoH delivers about 90% of the range it had when new. SoH is distinct from State of Charge (SoC), which is simply how full the battery is now. You manage SoC daily; SoH changes slowly over years.
Telematics-based methods, like the one Geotab uses across tens of thousands of vehicles, calculate SoH by measuring energy in during charging and energy out during driving, then tracking how capacity shifts over time. That real-world approach is more reliable than a one-off lab test because it reflects how the car is actually used.
What normal degradation looks like
The fear that EV batteries fail early is largely unfounded. Across a 22,700-vehicle dataset, average degradation came in at about 2.3% per year, leaving the average pack at roughly 81.6% of original capacity after eight years — comfortably above the 70% threshold most manufacturers warrant. In practice the battery usually outlasts your ownership, and a well-kept pack rarely becomes the reason a car is retired.
Degradation is also not linear. Most packs lose a little capacity quickly in the first months as the chemistry settles, then degrade much more slowly for years. A small early dip is normal, not a defect.
How to monitor your battery's health
- Use the car's own readout. Many EVs show battery health, usable capacity or a range estimate in the energy or service menus. Some require a service-mode check at a dealer.
- Run a periodic SoH check. Reputable third-party apps and OBD dongles can report SoH on many models, and independent battery-health certificates are available.
- Track real range over time. Note your typical range at 100% in similar conditions every few months. A steady, gradual decline is normal; a sudden drop is worth investigating.
- Watch for warning signs. Rapid capacity loss, a battery warning light, reduced charging speed or the car limiting power can all signal a problem — get it checked while under warranty.
- Keep records. Save SoH readings and service notes; they support warranty claims and boost resale value.
What ages a battery — and what to do about it
Lithium-ion packs wear from a mix of calendar age and use. The dominant operational driver in recent fleet analysis is charging power: vehicles relying on DC fast charging above 100 kW for more than 12% of sessions degraded at up to 3.0% per year — roughly double the rate of cars charged mainly on AC. Heat compounds the effect.
| Stressor | Effect | Practical habit |
|---|---|---|
| Heat | Speeds chemical ageing | Park in shade/garage; avoid repeated hot fast-charging |
| Very frequent DC fast charging | Up to ~2x faster degradation if overused | Use rapid charging for trips, not daily |
| Sitting at 100% or 0% | Adds calendar stress | Store at ~50–60%; set a daily charge limit |
| Deep full-empty cycling | Harder than shallow cycles | Top up little and often within a moderate band |
Daily charging: the 80% rule, kept current
The familiar advice is to keep the car between 20% and 80% for daily use. That still holds for NMC batteries (most longer-range EVs): set a daily limit around 80% and charge to 100% only before a long trip. Brief visits to 100% before driving have little lasting effect — it is sitting full for days that does harm.
LFP batteries (common in standard-range and many newer models) are different. Manufacturers generally recommend charging them to 100% regularly, partly because it helps the car estimate range and balance cells accurately. Follow your car's guidance rather than the generic 80% rule.
For a used EV the battery is the most valuable component. Ask for a State of Health reading, review the service and software-update history, and confirm how much battery warranty remains and whether it transfers. A documented SoH protects both buyer and seller.
Temperature and storage
Because heat is the main enemy, where you park matters. In hot weather use shade or a garage, and avoid fast-charging an already-hot pack repeatedly. In the cold, precondition while still plugged in so the car draws warmth from the grid, not the battery. If the car will sit unused for weeks, leave it at roughly 50–60% somewhere cool and use the charge-limit setting.
Frequently asked questions
How do I check my EV battery's state of health?
What is a normal EV battery degradation rate?
Does fast charging damage battery health?
Should I charge to 80% or 100%?
At what SoH should I worry?
Sources & further reading
- Geotab — EV Battery Health study (22,700 vehicles)
- Geotab — Battery health, fast charging & degradation study
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