Your EV Battery Health, Explained — and Protected

These two terms get confused constantly, but they measure completely different things. State of charge (SoC) is the number you see change every time you drive or plug in — it's how full the battery is right now, out of 100%, and it swings throughout the day. State of health (SoH) is a much slower-moving number: it's how much usable capacity the battery has left compared to when it rolled off the factory floor. A battery at 90% SoH simply can't hold as much energy at 100% SoC as it could when new — it's lost roughly a tenth of its total capacity, permanently.

SoC resets every charge cycle. SoH only moves in one direction, slowly, over years — which is exactly why it needs to be tracked over time rather than checked once. A single reading tells you almost nothing; a trend line tells you everything.

What actually degrades a battery

Four forces do almost all of the damage. Frequent DC fast charging generates heat and stresses the cell chemistry more than slow AC charging does — occasional use is fine, but making it a daily habit accelerates wear. Sitting at very high or very low states of charge for extended periods stresses the cells more than sitting in the middle of the range. Heat — both ambient and from charging — is the single biggest long-term accelerant of chemical degradation. And time itself causes a slow, unavoidable capacity loss even in a battery that's never driven, though normal use rarely makes this the dominant factor.

Battery chemistry matters

Not all EV batteries behave the same way. NMC (nickel manganese cobalt) chemistries, common in longer-range vehicles, generally prefer staying between roughly 20-80% for daily use and reserve 100% charges for trips. LFP (lithium iron phosphate) chemistries, increasingly common in standard-range and value-focused models, are more tolerant of regular 100% charges and don't degrade as quickly from it — some manufacturers actively recommend charging LFP packs to full regularly to keep the battery management system calibrated. Check your owner's manual for your specific chemistry before assuming either rule applies.

Most EV manufacturers back their battery with a warranty that guarantees a minimum state of health over a set period — commonly around 70% capacity retained across roughly 8 years or 160,000 km, though the exact numbers vary by brand, model and region, so check your specific documentation. The purpose of tracking your battery's health trend isn't just curiosity: it's knowing where you actually stand relative to that threshold, well before a warranty claim becomes relevant, and having the data to back up a claim if degradation ever looks abnormal.