EV Battery Glossary — Key Terms for Dealers
A quick-reference guide to the most important EV battery terms for UK car dealers. Each definition explains what the term means and why it matters when you're buying, certifying, or selling used electric vehicles.
State of Health (SoH)
A percentage score representing how much usable capacity a battery retains compared to when it was new. A brand-new battery is 100% SoH; a battery at 80% SoH has lost a fifth of its original capacity. This is the single most important metric for used EV valuation. Dealers who can prove SoH with an independent certificate — rather than relying on the dashboard estimate — command higher prices and reduce dispute risk. The AVILOO FLASH test delivers a TÜV-certified SoH reading in three minutes.
State of Charge (SoC)
The current charge level of the battery, shown as a percentage — essentially the EV equivalent of a fuel gauge. SoC tells you how much energy is available right now, but it says nothing about long-term battery condition. A battery at 90% SoC could still have poor State of Health. Dealers should never confuse a high charge level with a healthy battery. Buyers increasingly understand the difference, so transparent certification matters.
Cell Balancing
The process by which a Battery Management System equalises voltage across individual cells within a battery pack. Over time, cells degrade at different rates, creating imbalances that reduce range and performance. Poor cell balancing is one of the early warning signs of battery issues. The AVILOO test detects cell-level imbalances and flags them on the certificate heatmap, giving dealers visibility that a dashboard reading cannot provide.
OBD-2 / OBD Port
On-Board Diagnostics version 2 — a standardised diagnostic port fitted to all modern vehicles, usually located under the dashboard. The AVILOO Box plugs directly into this port to read battery data. No specialist tools, no vehicle disassembly, and no training required. The FLASH test runs entirely through the OBD-2 port in around three minutes on a stationary vehicle, making it practical to certify every EV on your forecourt.
Battery Management System (BMS)
The electronic controller that monitors and manages a battery pack's operation — regulating charging, discharging, temperature, and cell balancing. The BMS provides the dashboard estimates buyers see, but those estimates are manufacturer-derived and not independently verified. AVILOO's testing cross-references BMS data with its own TÜV-certified methodology to produce an independent State of Health reading that carries more weight with buyers and in legal disputes.
Kilowatt-Hour (kWh)
A unit of energy used to express battery capacity. A 77 kWh battery can theoretically deliver 77 kilowatts for one hour. Larger kWh figures generally mean longer range. For dealers, the usable kWh remaining (factoring in degradation) is what determines real-world range and, ultimately, the vehicle's market value. The AVILOO certificate shows remaining certified energy so buyers can compare like with like.
Cell-Level Analysis
A diagnostic approach that examines each individual cell within a battery pack, rather than just the pack as a whole. Battery packs contain hundreds or thousands of cells, and a single weak cell can limit overall performance. Cell-level analysis reveals hidden problems that pack-level readings miss — such as one module degrading faster than the rest. AVILOO's heatmap visualisation provides cell-level clarity on every certificate.
Pack-Level Analysis
A diagnostic approach that evaluates the battery as a single unit, reporting an overall health score without examining individual cells. Many cheaper testing tools only offer pack-level data. While useful as a quick indicator, pack-level analysis can mask localised problems — a pack might look healthy overall while one module is failing. For dealers, cell-level analysis offers far stronger protection against post-sale disputes.
TÜV Certification
TÜV (Technischer Überwachungsverein) is a group of German independent testing and certification bodies with global authority. AVILOO's battery testing methodology is certified by both TÜV Nord and TÜV Süd — the only battery health test in the world to hold dual TÜV certification. For dealers, this means the certificate carries independent, auditable authority. In the event of a Consumer Rights Act dispute, a TÜV-certified report is significantly stronger evidence than an uncertified opinion.
Battery Passport (EU)
A mandatory digital record of a battery's composition, origin, and health history, required under EU Battery Regulation from February 2027. While the UK is not directly bound by EU law post-Brexit, vehicles imported from Europe will carry Battery Passports, and UK regulation is expected to follow. Dealers who already certify battery health are building a data trail that aligns with where the market is heading. Early adoption means less disruption later.
Consumer Rights Act 2015 (as it relates to EVs)
UK legislation that gives buyers the right to reject goods that are not of satisfactory quality, fit for purpose, or as described. For used EV dealers, this creates a specific risk: if a battery degrades significantly within six months of sale, the burden of proof falls on the dealer to show the fault was not present at point of sale. A TÜV-certified battery certificate provides exactly this evidence — an independent, timestamped, auditable record of battery condition at the moment of transaction.
WLTP Range
Worldwide Harmonised Light Vehicle Test Procedure — a standardised lab test used to measure EV range. WLTP figures appear in manufacturer specs and on listings, but real-world range is always lower due to driving style, temperature, and battery degradation. The AVILOO certificate includes both WLTP-based range and real-world range estimates, helping dealers set accurate buyer expectations and reduce complaints.
DC Fast Charging
High-power charging that delivers direct current (DC) straight to the battery, bypassing the vehicle's on-board AC charger. DC fast charging enables rapid top-ups (often 10–80% in 20–40 minutes) but generates more heat than slower AC charging. Frequent DC fast charging can accelerate battery degradation over time, making a pre-sale battery health check more important for vehicles with heavy rapid-charging histories.
Thermal Management
The system that regulates battery temperature during charging, discharging, and ambient conditions. Liquid-cooled thermal management (used by Tesla, Hyundai, Kia, and others) generally preserves battery health better than air-cooled systems (used in early Nissan Leafs). Vehicles with poor thermal management tend to show faster degradation — a fact that a cell-level battery test will reveal clearly.
Battery Degradation
The gradual, irreversible loss of battery capacity over time and use. All lithium-ion batteries degrade — typically losing 1–3% capacity per year under normal conditions — but the rate varies dramatically by vehicle model, charging habits, climate, and thermal management quality. Degradation is the core risk in used EV sales. An independent SoH certificate quantifies exactly how much degradation has occurred, removing guesswork from pricing.
State of Certified Energy (SoCE)
An AVILOO-specific metric representing the independently certified remaining energy capacity of a battery, expressed in kWh. Unlike manufacturer dashboard estimates, SoCE is calculated using AVILOO's TÜV-certified methodology and appears on every certificate. For dealers, SoCE provides a concrete, comparable number: buyers can see exactly how many kWh the battery can actually deliver, making it easier to justify your asking price. Learn more about how the test works.
AVILOO FLASH Test
AVILOO's rapid battery health assessment designed for dealer workflows. The test takes approximately three minutes on a stationary vehicle — connect the AVILOO Box to the OBD-2 port, wait for data transmission, and receive a TÜV-certified certificate immediately. No driving required, no specialist training, and the test covers 95%+ of EVs and PHEVs on UK roads. The FLASH test is the tool dealers use to certify stock at scale.
AVILOO PREMIUM Test
AVILOO's comprehensive deep-dive battery assessment. The vehicle is driven from 100% to 10% charge over a period of up to seven days while the AVILOO Box continuously transmits data — including GPS and driving conditions. The result is a full State of Health certificate based on millions of data points, issued within two days. The PREMIUM test is ideal for high-value vehicles or situations where maximum buyer assurance is needed. Compare both test types on our How It Works page.
Heatmap (Battery Diagnostics)
A colour-coded visual representation of individual cell or module condition within a battery pack. Green cells are healthy; amber and red cells indicate degradation or imbalance. The heatmap appears on every AVILOO certificate and gives buyers an intuitive, at-a-glance view of battery condition. For dealers, the heatmap is a powerful sales tool — it turns invisible battery data into something a buyer can see and trust immediately.
Internal Resistance
A measure of how much a battery cell resists the flow of electrical current, expressed in milliohms. As cells age, internal resistance increases, reducing the battery's ability to deliver power efficiently — which means less range and slower performance. Elevated internal resistance in individual cells is an early indicator of degradation. AVILOO's cell-level analysis detects resistance anomalies that pack-level tests miss entirely.
Ready to Certify Your Stock?
Now you know the terminology, see how simple the process is. A three-minute test, a TÜV-certified certificate, and a stronger position on every sale.