EV Battery Degradation: What's Normal at 3, 5, and 8 Years

The question we get asked more than almost any other: "is this battery normal for its age?" It's a fair question, because degradation isn't linear and there's no single number that applies to every car. Here's what we actually see across the EVs that come through our workshop, broken down by age.

The general degradation curve

EV batteries don't degrade at a steady rate. Most lose a slightly larger chunk of capacity in the first year or two as the pack settles, then degrade more slowly and steadily for years afterward, before the rate can pick up again later in life as cells age unevenly. This "steeper start, flatter middle" pattern is why a 1-year-old car showing 97% and a 4-year-old car showing 91% can both be completely normal.

What's normal at 3 years

By three years, most well-cared-for EVs sit at 90–95% state of health (SOH). A car that's been fast-charged frequently, kept regularly at 100%, or driven hard in hot climates might sit at the lower end of that range, or occasionally a touch below. A car charged mostly at home, kept between 20–80% day to day, and used gently will often be at the higher end.

Usage pattern	Typical 3-year SOH
Gentle, mostly home AC charging	93–96%
Mixed use, occasional DC fast charging	89–93%
Heavy use, frequent DC fast charging, hot climate	84–90%

What's normal at 5 years

At five years, expect 83–91% SOH for a well-treated car under typical NZ conditions. This is usually the point where owners start noticing a real-world difference — a car that did 380 km on a full charge when new might now be doing 330–350 km. It's also roughly the midpoint of most manufacturer battery warranties (commonly 8 years/160,000 km), so this is a sensible time for your first proper health check if you haven't already had one.

Usage pattern	Typical 5-year SOH
Gentle, mostly home AC charging	87–91%
Mixed use, occasional DC fast charging	83–88%
Heavy use, frequent DC fast charging, hot climate	76–83%

What's normal at 8 years

Eight years is where things diverge more noticeably between cars, because small differences in charging habits and climate compound over time. Expect somewhere in the 72–85% SOH range for a car that's been reasonably looked after, with genuine outliers on both ends — well-treated packs occasionally still above 85%, and hard-used packs dropping toward or below the 70% threshold that most warranties use as a failure trigger.

Usage pattern	Typical 8-year SOH
Gentle, mostly home AC charging	80–85%
Mixed use, occasional DC fast charging	74–80%
Heavy use, frequent DC fast charging, hot climate	68–75%

What actually drives the difference

The spread between best-case and worst-case at the same age comes down to a handful of controllable factors:

• Charging habits. Regularly charging to 100% and letting it sit there (rather than charging shortly before departure) accelerates degradation on NMC-chemistry packs specifically.
• DC fast-charging frequency. Occasional fast charging is fine; doing it multiple times a week generates more heat cycling than the pack sees with gentle home charging.
• Climate. Consistently hot conditions age battery chemistry faster than NZ's generally mild climate — one advantage local owners have over EVs run in hotter countries.
• Depth of discharge. Regularly running the battery down near empty before charging stresses cells more than staying in a moderate 20–80% band.

When degradation is NOT normal

If your car is showing SOH noticeably below the ranges above for its age — say, a 3-year-old car already below 85%, or a sudden drop of several percentage points in a short period rather than a gradual decline — that's worth investigating properly rather than assuming it's just "how EVs age." Sudden drops can indicate a cell imbalance issue, which is often fixable if caught early and expensive if left.

What it means for your wallet at each stage

Degradation isn't just an abstract percentage — it has a practical cost timeline. At 3 years, most owners are still well within warranty and range loss is rarely noticeable day to day. At 5 years, it's worth budgeting mentally for the possibility of a partial module repair down the track, particularly if your SOH is tracking toward the lower end of the range for your usage pattern. At 8 years, if your pack is approaching the 70% threshold, it's sensible to start pricing out replacement options (reconditioned packs for common models often run $6,000–$11,000) so a future failure isn't a financial surprise, even if the car is still driving perfectly well today.

How to actually check

Don't rely on the dashboard's estimated range alone — it's affected by driving style, temperature, and recent trips, and isn't a reliable degradation indicator by itself. A proper battery health check ($140–$260 depending on diagnostic depth) reads the actual cell data and gives you a real SOH percentage plus any early warning signs of imbalance.

What this means for buying used

If you're shopping for a used EV, use these age brackets as a sanity check against the seller's claims, but always get an independent health check before you commit — the spread within each age bracket is wide enough that the age alone tells you surprisingly little. A well-documented 6-year-old car at 88% SOH can be a considerably better buy than a poorly-treated 4-year-old car at 82%, even though the younger car looks better on paper.