State of Charge (SoC) is how full your EV battery is at this moment, shown as 0 to 100% like a fuel gauge. State of Health (SoH) is the battery’s long-term condition compared to when it was brand new. A battery at 90% SoH has lost 10% of its original capacity. They sound similar, but they answer two very different questions.
Key takeaways
- SoC is a real-time reading of how much usable charge is left, from 0 to 100%.
- SoH compares current maximum capacity against the battery’s original capacity when new.
- A battery’s SoC changes minute to minute as you drive and charge; SoH only drifts down slowly over years.
- The Battery Management System (BMS) estimates both numbers, since neither can be measured directly.
- SoC decides today’s driving range. SoH decides how much range you lose over the years.
- SoH is the number that matters most for resale value and warranty claims.
What is State of Charge in an EV battery?
SoC is the fuel gauge of your EV. It tells you the percentage of usable energy left in the pack right now. At 100% the pack is full, at 0% it’s effectively empty. This number moves constantly. It drops as you drive, climbs back up when you charge, and even shifts slightly with temperature and how hard you accelerate. When you check your dashboard before a trip, the SoC is what you’re looking at.
What is State of Health in an EV battery?
SoH measures how much of the original capacity the battery still holds. Every lithium-ion pack degrades a little with each charge cycle and with age, so a three-year-old battery can’t store quite as much as it did on day one. If a battery started at 50 kWh and now tops out at 45 kWh, its SoH is roughly 90%. You won’t usually see SoH on your daily dashboard, but it’s the truest sign of how the battery is aging.
How does the BMS calculate both?
Neither SoC nor SoH can be read off a sensor directly, so the BMS estimates them. It tracks voltage, current flowing in and out, temperature, and charge cycles over time, then runs that data through software models. As pv magazine India explains , the BMS is the software brain that keeps the pack safe and performing well. If you want the full picture of how this controller works, see our guide on the intelligent BMS in India .
SoC vs SoH compared
Here’s how the two stack up side by side.
| Aspect | State of Charge (SoC) | State of Health (SoH) |
|---|---|---|
| What it measures | How full the battery is right now | Capacity left vs when new |
| Range | 0 to 100% | Starts near 100%, falls over time |
| How fast it changes | Minute to minute | Slowly, over years |
| Everyday analogy | Fuel gauge | Engine wear and tear |
| Why it matters to you | Today’s driving range | Resale, warranty, long-term range |
| Where you see it | Dashboard, app | Service report, diagnostic tools |
Which one should I worry about when buying a used EV?
SoH, without a doubt. SoC at the moment of sale tells you nothing useful, since you can charge the car back up in an hour. SoH tells you how much life the pack has left and how much range has already faded. A used EV with 95% SoH is in far better shape than one at 80%, even if both show a full charge. Most manufacturer warranties are also written around SoH, often guaranteeing the pack stays above a set percentage for a number of years. To understand what drives that decline, read our explainer on battery degradation in electric vehicles .
Can I improve my battery’s SoH?
You can’t reverse degradation, but you can slow it. Avoiding constant 100% charges, steering clear of frequent fast charging, and keeping the car out of extreme heat all help the pack hold its SoH for longer. The battery management system does a lot of this protection automatically, but your charging habits still make a real difference over the years.
Frequently asked questions
Is 90% SoH good for an EV battery?
Yes, 90% SoH is healthy. It means the pack has lost only about 10% of its original capacity, which is normal after a few years of use. Most EVs stay above 80% SoH well past the warranty period.
Does charging to 100% hurt my battery?
Charging to 100% occasionally is fine, especially before a long trip. Doing it every single day and leaving the car sitting fully charged speeds up degradation, which lowers SoH faster over time.
Why does my range drop in winter but my SoH stays the same?
Cold weather temporarily reduces usable SoC and range because the battery chemistry slows down. That’s a short-term effect, not permanent damage, so your SoH doesn’t change. Range usually returns once the battery warms up.
Can the BMS show me my exact SoH?
The BMS estimates SoH rather than measuring it directly, so the figure is an informed approximation. Service-grade diagnostic tools give a more accurate reading than the dashboard, which is why used-EV buyers often request a battery health report.
Sources
Last updated: 23 June 2026.
