Battery Charging and Charging Performance

Charging converts electrical energy from the grid or another source into chemical energy stored in an EV battery.

This chapter explains how energy reaches the battery, what determines charging power, and why two EVs connected to the same charger can perform differently; the underlying electrochemistry is covered in Battery Basics, while connectors, home charging, public infrastructure, bidirectional charging, and battery swapping are covered in the separate EV Charging guide.

Diagram showing ion and electron movement during EV battery charging — Ion and electron movement during battery charging

AC and DC Charging

An EV battery stores direct-current electricity. The main difference between AC and DC charging is where alternating current from the grid is converted into the direct current required by the battery.

AC Charging

During AC charging, the charge point supplies alternating current to the vehicle. The vehicle’s onboard charger converts that AC electricity into DC before it reaches the high-voltage battery.

A home wallbox is commonly called a charger, but most of its role is to provide:

A controlled electrical supply
Communication with the vehicle
Electrical protection
Cable and connector monitoring
Permission for current to flow

The power-conversion hardware is normally inside the vehicle. The US Department of Energy describes the onboard charger as the component that converts incoming AC electricity to the DC power needed by the traction battery. (Alternative Fuels Data Center)

A simplified AC charging path is:

Electrical grid
      ↓
AC charge point or wallbox
      ↓
Vehicle charge port
      ↓
Onboard charger: AC converted to DC
      ↓
High-voltage contactors
      ↓
Battery cells

Actual AC charging power is limited by the lowest applicable limit in the complete system:

Building supply
Number of electrical phases
Circuit and charge-point rating
Cable rating
Vehicle onboard-charger rating
Battery temperature and acceptance limit
Charging settings selected by the driver

A vehicle with an 11 kW onboard charger cannot use 22 kW from an AC charge point, even when the infrastructure can supply it.

AC Charging Is Normally Best for Long Parking Periods

AC charging suits situations where the vehicle will remain parked for several hours:

Home charging
Workplace charging
Hotel charging
Overnight destination charging
Long-term parking

Its lower power is usually sufficient when the vehicle has time to remain connected. It also avoids the cost and size of placing a high-power DC converter inside every car.

DC Fast Charging

During DC charging, the charging station performs the AC-to-DC conversion.

The station supplies regulated high-voltage DC through the vehicle’s charge port. The onboard AC charger is bypassed.

Electrical grid
      ↓
External DC charging station: AC converted to DC
      ↓
Vehicle charge port
      ↓
High-voltage contactors
      ↓
Battery cells

The station does not simply apply its maximum voltage and current. The vehicle and charging station communicate throughout the session. The vehicle requests suitable voltage and current based on the limits calculated by its battery and charging-control systems. The CCS charging sequence includes a requested DC voltage and current during precharge and subsequent charging communication. (CharIN)

The vehicle can reduce its request at any time because of:

Battery temperature
State of Charge
Cell voltage
Cell imbalance
Charging-port temperature
Battery current limit
Cooling performance
A detected fault

kW, kWh, and Charging Time

Charging discussions often confuse power and energy.

Kilowatts, or kW, describe how quickly energy is being transferred.
Kilowatt-hours, or kWh, describe how much energy is transferred or stored.
Charging time depends on the energy added and the average charging power.

A simplified relationship is:

Charging time ≈ Energy added ÷ Average charging power

Consider a vehicle that adds 49 kWh between 10% and 80% SOC.

If the process takes 18 minutes:

18 minutes = 0.3 hours

Average charging power =
49 kWh ÷ 0.3 h
= approximately 163 kW

The vehicle may briefly peak at 250 kW, but the average over the session is approximately 163 kW.

This is why peak charging power alone does not describe charging time.

What Determines Actual DC Charging Power?

Actual charging power is the result of several limits acting at the same time.

It can be approximated as:

Actual charging power =
The lowest applicable charger, connector,
vehicle, and battery limit

Charger-Side Limits

The charging station can be limited by:

Maximum total power
Maximum output voltage
Maximum output current
Cable and connector temperature
Power-module temperature
Site connection capacity
Battery storage or grid limits
Power sharing between charge points
Temporary thermal derating

A charger marketed as 350 kW does not necessarily deliver 350 kW at every combination of voltage and current. Charging equipment operates within a defined voltage-current envelope, not at one fixed power in every situation. CharIN’s DC power classes therefore specify both voltage and current capabilities. (CharIN)

Vehicle-Side Limits

The vehicle can be limited by:

Battery voltage
Maximum battery current
Maximum charging power
Cell temperature
State of Charge
Highest cell-group voltage
Internal resistance
Cell imbalance
Cooling-system capacity
Charge-port temperature
High-voltage cable and busbar limits
BMS charging strategy

The result shown on the charger is whichever limit is lowest at that moment.

Example

An EV may support:

500 kW maximum battery power
800 A maximum battery current

But the connected charger may provide only:

350 kW maximum power
500 A maximum current

The vehicle cannot reach its advertised maximum because the charger becomes the limiting component.

The Charging Curve

A charging curve plots charging power against battery State of Charge.

The curve is not flat because battery voltage, cell condition, temperature, and safe current limits change as charging progresses.

Communication, Precharge, and Ramp-Up

Before high current begins, the vehicle and station:

Establish communication
Lock the connector
Verify electrical isolation
Agree on voltage and current limits
Precharge the vehicle’s high-voltage circuit
Close the battery contactors
Begin increasing current

The first seconds of a session are therefore not representative of the battery’s full charging capability.

Some EVs ramp rapidly to peak power. Others increase more gradually because of thermal conditions, charger behaviour, or BMS strategy.

Low-SOC Charging

At low SOC, the battery usually has considerable voltage headroom, but maximum power can still be restricted by:

A cold battery
Charger current limits
Low pack voltage
Cell-current limits
Initial BMS ramp-up strategy

A high-voltage-class battery may not achieve high power at very low SOC if the charger reaches its current limit before reaching its advertised power rating.

High-Power Region

The strongest part of the curve may be controlled by current, power, or temperature.

Constant-Current Behaviour

If charging current remains approximately constant while battery voltage rises, charging power rises:

Power = Voltage × Current

Constant-Power Behaviour

If the system holds power approximately constant while battery voltage rises, current must gradually decrease.

Thermal Limiting

The BMS may reduce current if:

Cell temperature rises too quickly
The cooling system reaches its capacity
The charge port or connector becomes hot
A particular module or cell group is warmer than the rest

This can create visible steps or reductions in the charging curve.

High-SOC Taper

As the battery fills, the highest-voltage cell groups approach their upper limit.

The BMS must reduce current to prevent any monitored group from exceeding its permitted voltage. The reduction is known as the charging taper.

The taper can be influenced by:

Cell chemistry
Cell resistance
Battery temperature
Cell imbalance
Upper buffer strategy
Charging-current limits
Cooling capability

The final percentages often take disproportionately long because charging current becomes low near the upper operating limit.

Peak Power Versus Average Power

Peak power describes the highest power observed during the session.

Average power describes how quickly energy is added across a chosen SOC window.

A car that reaches 400 kW for one minute and then rapidly falls below 150 kW may take longer from 10% to 80% than a vehicle that holds approximately 250 kW across most of the same window.

Useful comparisons include:

Peak charging power
Average power from 10% to 80%
Average power from 10% to 100%
Energy added in 10, 15, or 20 minutes
Time from 10% to 80%
Charging power at 50%, 70%, and 80% SOC
Repeatability at later charging stops

Peak Power Is Not the Same as Road-Trip Performance

Charging performance should be judged together with vehicle efficiency.

A vehicle adding 60 kWh in 20 minutes but consuming 30 kWh/100 km gains approximately 200 km of energy under the assumed conditions.

A more efficient vehicle adding 50 kWh in the same time while consuming 20 kWh/100 km gains approximately 250 km.

For a long journey, useful charging performance depends on:

Energy added per minute
             ÷
Energy consumption per kilometre

This is why range added per minute can be useful when the underlying consumption assumptions are clear.

Manufacturer claims based on laboratory range should not be compared directly with real-world charging tests unless both use the same range and consumption basis.

Charging C-Rate

C-rate compares charging power with battery capacity.

An approximate charging C-rate is:

Charging C-rate =
Charging power in kW ÷ Battery capacity in kWh

Examples:

Battery capacity	Charging power	Approximate C-rate
100 kWh	100 kW	1C
100 kWh	250 kW	2.5C
50 kWh	250 kW	5C

The same 250 kW charging power is much more demanding for the 50 kWh battery than for the 100 kWh battery.

This is a simplified comparison. Battery voltage changes through the session, and manufacturers may calculate C-rate using gross capacity, usable capacity, nominal ampere-hour capacity, or a particular operating point.

Voltage and Current

Charging power is calculated as:

Power = Voltage × Current

At an idealised 500 A:

Battery voltage	Power at 500 A
400 V	200 kW
800 V	400 kW
1,000 V	500 kW

These values are illustrative.

An “800-volt” battery does not remain at exactly 800 V. Actual pack voltage changes with:

SOC
Chemistry
Number of series-connected cells
Temperature
Current
Manufacturer voltage limits

A nominally 800-volt-class battery may operate substantially below 800 V through much of the charging session.

Current-Limited Charging

Current has become one of the most important limits for the latest high-power EVs.

Consider a charger limited to 500 A.

At an actual battery voltage of 700 V:

Power = 700 V × 500 A
      = 350 kW

An EV capable of more than 500 kW cannot reach that power on the charger, even if both the car and station are marketed as high-voltage systems.

Higher current requires:

Larger conductive paths
Lower-resistance connections
Stronger connector cooling
More capable liquid-cooled cables
Better temperature monitoring
High-current contactors and busbars

A charger’s headline power rating therefore needs to be considered together with its maximum current.

400-, 800-, and 1,000-Volt-Class Charging

The detailed vehicle-architecture differences are covered in Battery Pack & Configuration.

For charging, the main advantage of higher voltage is that the same power can be delivered at lower current.

400-Volt-Class Batteries

A well-engineered 400-volt battery can charge quickly, particularly when it has:

High current capability
Strong cooling
Low cell resistance
A broad charging plateau
A sufficiently capable charger

Its main challenge is reaching very high power without extreme current.

800-Volt-Class Batteries

An 800-volt-class battery can reach high charging power while staying within lower current levels than an equivalent 400-volt system.

This can reduce:

Cable losses
Connector heating
Busbar losses
Cooling demand in conductors

It does not automatically improve the cell charging C-rate or guarantee a better charging curve.

1,000-Volt-Class Batteries

Newer platforms are moving beyond the established 800-volt class.

BYD’s 2025 Super e-Platform was announced as a full-domain 1,000-volt architecture with a claimed 1,000 A battery charging current, 10C charging rate, and 1 MW peak charging power. The first announced vehicles were the BYD Han L and Tang L. BYD also announced a liquid-cooled charging terminal capable of up to 1,360 kW. (BYD)

These figures require both a compatible vehicle and new charging infrastructure. A 1 MW-capable battery connected to a conventional 500 A charger will remain current-limited.

Charging an 800-Volt Battery on Lower-Voltage Hardware

An 800-volt battery cannot charge directly from a station whose maximum output voltage is below the battery voltage.

Manufacturers use several approaches.

Dedicated Voltage Booster

A DC-DC boost converter raises the station voltage to the level needed by the battery.

This provides broad compatibility but adds:

Cost
Weight
Packaging
Conversion losses
Cooling requirements

Motor and Inverter Used for Voltage Boosting

Hyundai Motor Group’s E-GMP architecture uses the traction motor and inverter as part of the voltage-conversion system when connected to lower-voltage DC charging hardware.

Hyundai states that the system boosts a 400 V charging input to the voltage needed by the 800 V battery without requiring a separate external adapter. (Hyundai)

The result provides compatibility, but charging power on the lower-voltage station may remain below what the vehicle can achieve on suitable high-voltage infrastructure.

Bank Charging

Another strategy is to reconfigure the battery electrically into two lower-voltage sections.

The Audi Q6 e-tron and Porsche Macan Electric can divide their 800-volt-class batteries into two approximately 400-volt banks. The banks are then charged in parallel.

Audi and Porsche specify up to 135 kW when using this method on suitable 400-volt charging equipment. The Macan does this without a separate high-voltage booster. (Audi)

Bank charging changes the electrical connection between pack sections. It does not physically split or move the battery cells.

Battery Temperature

Battery temperature strongly affects charging performance.

A cold battery has:

Higher resistance
Slower ion movement
Greater voltage rise under charging current
Increased risk of lithium plating
Lower permitted charging current

A battery that is too hot may also receive less power because the BMS must prevent excessive cell temperature and degradation.

The preferred charging-temperature window varies between chemistries and vehicle designs.

Battery Preconditioning

Preconditioning heats or cools the battery before arriving at a fast charger.

Activation methods can include:

Selecting a charger in the onboard navigation system
Automatic route planning
Manual battery-preparation controls
A scheduled departure
Software prediction based on expected charging

Preconditioning does not guarantee peak power. The vehicle still needs:

Enough preparation time
A suitable arrival SOC
A compatible charger
Acceptable cell balance
Sufficient cooling capability

The system is explained in detail in Battery Thermal Management.

BMS Charging Strategy

The Battery Management System continuously calculates the maximum voltage and current the battery can accept.

Its decision is based on values such as:

Highest cell-group voltage
Battery temperature
Cell resistance
State of Charge
Cell imbalance
Battery State of Health
Cooling capability
Fault status

The BMS communicates those limits to the vehicle’s charging controller. The vehicle then requests suitable power from the station.

This is why two vehicles with similar battery capacity and voltage can have very different charging curves.

Manufacturers can choose different priorities:

Maximum short-term charging power
A broad, repeatable charging plateau
Lower battery temperature
Conservative cell-voltage limits
Long-term durability
Compatibility with a wider range of chargers

A software update can change charging behaviour without changing the battery cells or charging hardware.

Charging Losses

The battery stores less energy than the charging installation draws from the grid.

Energy is lost in:

Charging-station power electronics
Onboard charger during AC charging
Cables and connectors
Vehicle conductors
Battery resistance
Cooling pumps and fans
Air-conditioning compressor
Battery heaters
Low-voltage electronics

During AC charging, conversion losses in the onboard charger can be a significant part of the difference.

During DC charging, the station performs the main AC-to-DC conversion, but energy is still consumed by the battery and vehicle thermal systems.

The number shown by the station can represent energy delivered at the station output rather than energy finally stored chemically in the cells.

See the EVKX Charging Loss article for a detailed breakdown.

Repeated Fast Charging

One strong charging session does not guarantee the same result at the next stop.

Heat accumulates in:

Cell interiors
Cooling plates
Coolant
Busbars
Charge-port contacts
Battery enclosure
Power electronics

The thermal system must:

Remove heat during charging
Continue cooling after departure
Prepare the battery for the next stop
Prevent large temperature differences across the pack

A vehicle with a lower peak but strong repeatability may complete a long trip faster than one that achieves a spectacular first session and then slows significantly.

Repeated charging performance is particularly relevant during:

Summer motorway journeys
Autobahn driving
Towing
Mountain routes
Successive high-power stops
High ambient temperature

How to Compare Charging Performance

A useful charging comparison should include more than one number.

Relevant Metrics

Compare:

Peak charging power
10–80% time
Energy added from 10% to 80%
Average charging power
Charging power at higher SOC
Approximate peak and average C-rate
Charger voltage and current requirements
Cold-weather performance
Preconditioning support
Repeated-stop performance
Vehicle efficiency

Use the Same SOC Window

A 10–80% claim cannot be compared directly with:

20–80%
10–70%
10–90%
30–80%

The energy transferred is different.

A five-minute 10–70% result may be outstanding, but it does not describe the time needed to reach 80%, 90%, or 100%.

Compare Energy, Not Just Percentage

Adding 60% to a 120 kWh battery represents more energy than adding 60% to a 60 kWh battery.

This is why average charging power and kilowatt-hours added provide essential context.

Check Charger Requirements

A charging curve may require:

More than 500 A
More than 800 V
A proprietary charger
A specially cooled cable
A charger that does not share power
Battery preconditioning

A vehicle that charges exceptionally on one charger may perform very differently on the existing public network.

Read EVKX Charging Curves Carefully

EVKX provides charging curves for individual vehicle variants.

Each curve should be read together with:

Battery variant
Source and test conditions
Starting battery temperature
Charger capability
SOC window
Whether power was measured or manufacturer-claimed
Any alternate current-limited scenarios

A curve recorded under optimal conditions is not a guarantee that every charging session will reproduce it.

Current High-Power Charging Examples

The examples below show different stages of high-power charging development. Additional EVKX model curves can be added to illustrate strong 400-volt systems, established 800-volt charging, moderate but flat curves, and charger-current limitations.

XPENG X9: High-Current 800-Volt Charging

The European XPENG X9 is a useful example of how battery C-rate, pack voltage, and charger current capability now converge.

XPENG’s 2026 German specifications list:

800-volt architecture
5C charging
Up to 537 kW for the 94.8 kWh LFP Standard Range
Up to 542 kW for the 110 kWh NCM Long Range and Performance
20–80% in a claimed ten minutes

Other regional XPENG material quotes 10–80% in 12 minutes, so the exact SOC window and homologated specification should be identified for the market and vehicle variant being described. (XPENG)

At 800 V, 542 kW corresponds to approximately 678 A:

Current = 542,000 W ÷ 800 V
        = approximately 678 A

Actual battery voltage can be below 800 V, requiring even more current. A charger limited to 500 A therefore cannot reproduce the vehicle’s full charging power.

The X9 is a strong example of why the next charging bottleneck is often current capability rather than the charger’s headline power alone.

BYD Super e-Platform: 1 MW

BYD introduced the first generation of its megawatt passenger-car charging system in 2025.

The manufacturer claims:

Full-domain 1,000-volt architecture
1,000 A charging current
10C peak charging rate
1,000 kW peak charging power
400 km of claimed range added in five minutes
Charging hardware capable of up to 1,360 kW

The first announced vehicles were the BYD Han L and Tang L. (BYD)

These are manufacturer claims under specified conditions. They do not describe charging on ordinary public chargers.

Blade Battery 2.0 and 1.5 MW Flash Charging

In 2026, BYD announced a second generation of its Blade Battery and Flash Charging technology.

For the new Denza Z9 GT implementation, BYD claims:

Up to 1,500 kW through one charging connector
10–70% in five minutes
10–97% in nine minutes
20–97% in 12 minutes at −30°C
A battery capacity of approximately 122 kWh

BYD’s announcement connects the highest 1,500 kW figure with its latest dedicated Flash Charging station and notes a Chinese-market single-cable implementation. The European infrastructure version and independently measured charging curve remain important points to verify as the system launches. (BYD)

The 2026 Flash Charging Z9 GT should not be treated as electrically identical to earlier Z9 GT variants. The battery generation and charging system need to be identified separately when presenting EVKX charging data.

Megawatt Charging Does Not Mean Every Stop Takes Five Minutes

Megawatt charging can reduce the battery-connected portion of a stop, but the complete experience also includes:

Entering the charging site
Finding an available compatible charger
Connecting the cable
Authentication and payment
Charging-system startup
Reaching the desired SOC
Disconnecting and leaving

The highest charging claims also depend on:

A specific starting SOC
A prepared battery
Compatible infrastructure
No charger derating
No site power limitation
Suitable battery temperature
The vehicle following its claimed curve

These systems bring battery charging time closer to a conventional fuel stop under ideal conditions, but they do not make all charging sessions equivalent to refuelling.

What Matters on a Long Journey

The best charging vehicle is not necessarily the one with the highest number in its brochure.

The most useful system combines:

A battery that accepts high power
A broad charging curve
Efficient thermal management
Reliable preconditioning
Compatibility with available chargers
Strong repeatability
Low energy consumption
Clear route planning

Peak power helps with short low-SOC stops. Average power determines how quickly energy is added. Vehicle efficiency determines how far that energy takes the car.

Charging performance is therefore a property of the complete vehicle, battery, charger, and journey—not one isolated kilowatt figure.