Charging curves are graphs or profiles that show how an EV’s charging power (kW) or charging current changes over time or as the battery state of charge (SoC) increases. They explain why charging is fast at low SoC and slows down as SoC increases, and they are critical for planning charging sessions, site throughput, and fleet readiness.
What Are Charging Curves?
A charging curve describes the relationship between:
– SoC (%) and charging power (kW)
– Or time and charging power (kW)
– Sometimes voltage and current across the session
Charging curves are determined mainly by the vehicle’s Battery Management System (BMS), which controls how much power the vehicle will accept to protect the battery.
Why Charging Curves Matter in EV Charging
Charging curves matter because they define real-world charging performance, not the charger’s headline rating. They:
– Determine session duration and charging speed perception
– Influence bay turnover and charge throughput at public sites
– Affect fleet schedules and readiness planning
– Explain charge tapering and why 80–100% can take a long time
– Help operators size sites and plan charging capacity planning
– Support troubleshooting by separating EV-limited vs site-limited behavior
Two vehicles on the same charger can have very different charging curves.
How Charging Curves Work
Most EVs follow a pattern broadly similar to a CC-CV charging profile:
– Early phase: higher power at low SoC (strong charge acceptance)
– Mid phase: power may stay high if thermal conditions allow
– Transition: power begins to drop as battery voltage approaches limits
– Late phase: power tapers down (CV region), especially at high SoC
The exact curve depends on vehicle strategy and conditions.
What Shapes a Charging Curve
Charging curves are influenced by multiple factors:
– Battery chemistry and pack design
– Thermal performance and battery thermal limits
– Ambient temperature and battery preconditioning
– Battery age and battery aging (internal resistance changes)
– Starting SoC (arriving at 60% vs 10% changes the session experience)
– Charger type (AC vs DC) and voltage/current capability
– Cable and connector limits
– Site power constraints and active power throttling
– Load sharing on multi-connector chargers
Charging Curves in AC vs DC Charging
– AC charging curves
– The vehicle’s onboard charger limits power (often 3.7–11 kW, sometimes 22 kW)
– Curve is often flatter, but still tapers near full
– DC fast charging curves
– The curve is more dynamic and visible due to higher power levels
– Early high power can drop significantly due to tapering or thermal limits
Typical Use Cases
– Public DC hubs optimizing bay turnover and reducing queues
– Fleet depots setting charging targets (e.g., charge to 80% by 05:00)
– Customer dashboards showing expected charging time and power behavior
– Network planning using real vehicle curves to estimate real throughput
– Troubleshooting “slow charging” by comparing delivered power to expected curves
Key Benefits of Understanding Charging Curves
– More accurate user expectations and fewer frustration cases
– Better site sizing and reduced overbuild/underbuild risk
– Improved operational policies (SoC targets, idle fee strategies)
– Better fleet scheduling and improved readiness reliability
– More accurate ROI and throughput modeling
Limitations to Consider
– Charging curves vary widely by vehicle model and battery condition
– Publicly available curves may not reflect real conditions (temperature, battery preconditioning)
– Chargers may be constrained by site limits, which distorts observed curves
– Using average curves can hide worst-case vehicles and peak congestion days
– Data access can be limited without vehicle telemetry integration
Related Glossary Terms
Charging Curve
CC-CV Charging Profile
Charge Tapering
Charge Acceptance Rate
State of Charge (SoC)
Battery Management System (BMS)
Battery Thermal Limits
Active Power Throttling
Charge Throughput
DC Fast Charging