Charging tapering is the controlled reduction of charging power as an EV battery approaches a higher state of charge (SoC). It happens because the battery management system (BMS) limits current to protect battery health, manage heat, and maintain safe cell voltage—especially near 80–100% SoC. Tapering is a normal part of EV charging behavior and is one of the main reasons charging from 80% to 100% takes disproportionately longer than charging from 20% to 80%.
What Is Charging Tapering?
Charging tapering occurs when an EV transitions from delivering high power early in a session to lower power later. Even if a charger can supply more power, the vehicle may request less due to battery constraints.
Tapering is most visible in DC fast charging, but it can also appear in AC charging depending on the vehicle’s onboard charger, thermal limits, and SoC targets.
Why Charging Tapering Matters
Charging tapering affects both user experience and charging network economics:
– Impacts session duration and perceived “charging speed”
– Reduces site throughput and charger utilization efficiency at high SoC
– Influences pricing fairness under time-based tariffs
– Shapes queueing, dwell time, and station congestion at busy locations
Understanding tapering helps operators set realistic expectations and optimize pricing, signage, and site planning.
How Charging Tapering Works
Most EVs follow a battery-friendly charging profile:
– High power at low-to-mid SoC (battery can accept more current safely)
– Gradual power reduction as SoC rises (cell voltage increases, heat risk increases)
– Stronger taper near the top end (80–100%) to avoid overvoltage and degradation
This behavior is governed by the BMS, which continuously monitors:
– Cell voltage and balance
– Battery temperature
– Internal resistance and charge acceptance
– Safety thresholds and long-term degradation limits
The charger delivers the power the vehicle requests, within its capability.
CC-CV Charging Profile and Tapering
Charging tapering is closely tied to the CC-CV (constant current – constant voltage) charging approach used for lithium-ion batteries:
– In the constant current phase, power is high and relatively stable
– In the constant voltage phase, voltage is held constant and current decreases
The current decrease in the CV phase is the core mechanism behind tapering.
Factors That Influence How Strong Tapering Is
Tapering severity varies between vehicles and conditions. Key drivers include:
– Battery chemistry and pack design
– Battery temperature (cold batteries taper earlier and more aggressively)
– Starting SoC (high SoC from the start often means immediate taper)
– Battery preconditioning (warming improves charge acceptance)
– Charger power level vs vehicle max acceptance (a 150 kW charger won’t help a car capped at 70 kW)
– Cell balancing behavior near high SoC
As a result, two vehicles on the same charger can show very different power curves.
Practical Impact on Charging Time and Throughput
Because tapering reduces average power over the session:
– The “peak kW” number is not the same as real-world average kW
– The final 20% can add a large share of total time
– Busy charging sites can see reduced turnover if many drivers charge to 100%
For site planning, throughput is often better predicted using average delivered power and typical SoC targets rather than charger nameplate power.
How Operators Use Tapering Insights
Operators and site hosts often adapt operations based on tapering behavior:
– Encourage charging to 80% at high-traffic sites to improve turnover
– Use idle fees or parking integration to prevent long occupancy after charging completes
– Prefer €/kWh pricing over time-based pricing where possible to improve fairness
– Educate users through app UX and on-site messaging about expected power reduction
These strategies help improve both user experience and site economics.
Related Glossary Terms
CC-CV Charging Profile
Charge Acceptance Rate
Charging Curves
State of Charge (SoC)
Battery Management System (BMS)
DC Fast Charging
Charging Dwell Time
Charger Utilization Rate
Demand-Based Pricing
Idle Fees