BEST PRACTICES FOR
PAYMENT SYSTEMS
at Public Electric Vehicle
Charging Stations
FEBRUARY 2024
ii
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Authors
Kristi Moriarty ([email protected]) and John Smart ([email protected])
Contributors
AMPECO, AmpUp, Bluedot, BMW, ChargeHub, ChargePoint, Electrify America, EVgo, FLO,
General Motors, Hubject, Nayax, Payter, Rivian, and Siemens.
Acknowledgments
The National Charging Experience Consortium (ChargeX Consortium) is a collaborative effort
between Argonne National Laboratory, Idaho National Laboratory, National Renewable Energy
Laboratory, electric vehicle charging industry experts, consumer advocates, and other
stakeholders. The Payment & User Interface Task Force in Working Group 2:
Reliability/Usability Triage developed this document.
The authors would like to acknowledge the Joint Office of Energy and Transportation (Joint
Office) for supporting this work. The Joint Office and national laboratory staff would like to
recognize the invaluable contribution of industry partners in providing the input summarized in
this report.
Disclaimer
This report was prepared for the U.S. Department of Energy (DOE) under DOE M&O Contract
No. DE-AC36-08GO28308 and DOE Idaho Operations Office Contract No. AC07-05ID14517.
Funding was provided by the Joint Office of Energy and Transportation. This information was
prepared as an account of work sponsored by an agency of the U.S. Government. Neither the
U.S. Government nor any agency thereof, nor any of their employees, makes any warranty,
expressed or implied, or assumes any legal liability or responsibility for the accuracy,
completeness, or usefulness, of any information, apparatus, product, or process disclosed, or
represents that its use would not infringe privately owned rights. References herein to any
specific commercial product, process, or service by trade name, trademark, manufacturer, or
otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring
by the U.S. Government or any agency thereof. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the U.S. Government or any agency thereof.
iii
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
List of Acronyms
ChargeX Consortium National Charging Experience Consortium
CSO charging station operator, also referred to as a charge point operator (CPO)
eMSP e-mobility service provider
EV electric vehicle
EVSE electric vehicle supply equipment
NFC near-field communication
PCI payment card industry
QR quick response
RFID radio frequency identification
SIM subscriber identity module
SMS short message/messaging service
iv
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Table of Contents
1 Introduction ........................................................................................................................................... 1
1.1 EV Charging Payment Methods .................................................................................................... 1
1.1.1 Credit Card Readers ......................................................................................................... 1
1.1.2 RFID ................................................................................................................................. 1
1.1.3 NFC .................................................................................................................................. 2
1.1.4 Apps ................................................................................................................................. 2
1.1.5 Plug & Charge .................................................................................................................. 2
1.1.6 Phone Call, Text, or SMS ................................................................................................. 2
1.2 Methodology and Resources ......................................................................................................... 2
2 Network .................................................................................................................................................. 3
3 Integration, Activation, and Installation ............................................................................................. 5
4 Robustness of Hardware ..................................................................................................................... 6
5 Customer Experience ........................................................................................................................... 7
6 Maintenance .......................................................................................................................................... 9
7 Other ...................................................................................................................................................... 9
8 Conclusion .......................................................................................................................................... 10
References ................................................................................................................................................. 11
v
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
List of Tables
Table 1. Network Issues and Proposed Solutions ......................................................................................... 3
Table 2. Integration, Activation, and Installation Issues and Proposed Solutions ........................................ 5
Table 3. Robustness of Hardware Issues and Proposed Solutions ................................................................ 6
Table 4. Customer Experience Issues and Proposed Solutions ..................................................................... 7
Table 5. Maintenance Issues and Proposed Solutions .................................................................................. 9
Table 6. Other Issues and Proposed Solutions .............................................................................................. 9
1
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
1 Introduction
Failure to accept and process payment is a cause of public electric vehicle (EV) charging session
failures. This document summarizes EV charging payment challenges and proposed solutions.
Data are not available to rank the severity of payment issues; however, input from members of
the National Charging Experience Consortium (ChargeX Consortium) suggests that payment
issues present ongoing challenges. The input also indicates that credit card readers have been
more prone to failure than other payment methods. The multiple EV charging payment options
commonly provided for customers at public charging stations increase the complexity in solving
the issue. This document considers the following forms of payment: credit card readers, radio
frequency identification (RFID), near-field communication (NFC), apps, Plug & Charge, and
phone call, text, or short message service (SMS).
1.1 EV Charging Payment Methods
There are multiple methods to pay for an EV charging session. The flexibility allows customers
various options to address the needs of different customers and to offer backup options if a
preferred method fails. Most methods depend on a network connection to authenticate payment
and allow the charging session to start. All methods of payment can be impacted when a
customer has an invalid credit or debit card or payment information stored in an account. Credit
card, NFC, and RFID reader hardware are subject to durability, environmental, and vandalism
impacts. The authors are unaware of an EV station that accepts cash payment.
1.1.1 Credit Card Readers
Credit card readers at public EV charging stations allow customers to pay for charging using
credit and debit cards. A customer can generally insert, swipe, or tap a credit or debit card to pay.
This method of payment is familiar, convenient, and accessible for many customers. The
National Electric Vehicle Infrastructure Formula Program and other federal and state programs
require card readers. Card readers for insert and swipe methods of payment are exposed to dirt,
dust, rain, snow, and ice, as well as vandalism. Issues with payment can be due to an inoperable
card reader, network connection issues, or an invalid or expired credit or debit card.
1.1.2 RFID
RFID is a wireless communication method that allows customers to pay for charging directly
from their charging network account. They do this by holding a charging network membership
card near an RFID reader,
1
transmitting account information via the card’s embedded chip and
antenna. RFID cards are also a form of prepaid card made available by fleet operators and
charging station operators (CSOs). Most RFID cards follow the International Organization for
Standardization (ISO) 14443 standard for communication with the reader. A card’s unique
identifier is shared with the electric vehicle supply equipment (EVSE) and sent to the charging
network provider for authorization, which will be granted if it belongs to an authorized member
of the network. Issues with RFID payment are generally due to a customer account storing an
1
There are various implementations of payment hardware on EVSE—RFID may be incorporated into a credit card
reader or it may be a stand-alone RFID reader.
2
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
invalid or expired credit or debit card, lack of funds for prepaid cards, or network connection
issues.
1.1.3 NFC
NFC, a subset of RFID, is a wireless communication method that enables contactless payment
via credit or debit card, smartphone apps (e.g., Apple Pay, Google Wallet, Samsung Pay),
wearables, and other contactless payment cards. Credit card readers are typically NFC-enabled,
or there can be a separate NFC device on the EVSE. NFC payment issues are generally due to a
customer account storing an invalid or expired credit or debit card or network connection issues.
1.1.4 Apps
Charging station, roaming, and vehicle apps allow a customer to store their credit and/or debit
card information for payment at a station. Issues with app payment are generally due to a
customer account storing an invalid or expired credit or debit card or customer cellphone
connection strength.
1.1.5 Plug & Charge
Plug & Charge automates communication and payment between the vehicle and charging station.
An e-mobility service provider (eMSP) is an organization that provides EV charging roaming
service and is a required part of the Plug & Charge ecosystem. The customer has credit and/or
debit card information stored in their account, which is used to authorize and pay for a charging
session. Issues with Plug & Charge payment are generally due to a customer account storing an
invalid or expired credit or debit card or EVSE network issue. Issues with public key
infrastructure security certificates may also contribute to failed authorizations. Additionally,
inconsistent implementation of Plug & Charge may also prevent authorizations. Even if a
customer’s EV is capable of Plug & Charge, authorization will fail if the charger is not capable
of this method of payment, or due to varied implementation of ISO 15118, the communication
standard that defines Plug & Charge.
1.1.6 Phone Call, Text, or SMS
CSOs offer customer support and payment through a toll-free phone number or allow text/SMS
for assistance with payment and remotely starting a charging session. This provides a payment
option for customers without smartphones, preestablished membership accounts, or payment
cards. It also provides a backup option if a customer encounters an issue with payment by other
methods.
1.2 Methodology and Resources
A literature review found survey data stating that there are payment challenges for EV charging;
however, no comprehensive documents were found detailing the issues. The approach for this
report included input from ChargeX Consortium members through one-on-one meetings, which
served as a starting point to identify issues and, in some instances, potential solutions. The
ChargeX Consortium’s Payment & User Interface Task Force members refined the issues list
and provided proposed solutions. Ongoing meetings, reviews, edits, and comments from the task
force refined the information included in this document. The content is separated into key topic
sections, and a table within each section groups issues and proposed solutions.
3
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Useful references include the two publications issued by the U.S. Payments Forum EV Open
Payments Working Committee on the use of the correct merchant category code and terminal
payment flow guide (U.S. Payments Forum 2024).
2 Network
All forms of payment rely on various forms of network connections to enable charging. Card,
NFC, and RFID readers either have their own network connection or are tied into the EVSE
network connection. This section focuses on card, NFC, and RFID reader network connections.
However, it is also applicable to EVSE network connections necessary for app and Plug &
Charge payment methods.
Table 1. Network Issues and Proposed Solutions
Issues Proposed Solutions
Network Strength
Poor network connectivity of payment
systems is a significant issue.
a
The U.S. cellular network generally lacks
robustness. The United States has a
patchwork of overlapping cellular networks
run by three major networks with spotty
coverage outside of urban areas.
EVSE located outside urban areas suffers
from chronic connectivity issues.
EVSE and mobile phone connectivity at
stations located in underground garages is
poor.
Customer’s phone shows good connectivity
but data is not working.
Payment system could be online but with
high latency and low connectivity.
b
CSO and site hosts conduct site survey for cellular
connectivity and analyze site factors that may cause
signal interference or lessen reception. Signal strength
should be tested at different days and times (including
weekdays and weekends) and tested at each
maintenance visit.
Designate standard for minimum connectivity level
inclusive of network speed.
Use dedicated subscriber identity module (SIM) cards
for the strongest signal at the station location; use a
backup, multi-network (roaming) SIM card if the
configuration allows for a second SIM.
Use ethernet connection where possible for hardwire
connection to a modem or router.
c
• Run ethernet cable through a separate conduit
than power lines.
• Include a cellular modem and SIM card as a
backup network connection.
• Not all locations will have ethernet as an
option, and it adds significant expense.
• Caution: CSOs may encounter scaling issues
with having different connectivity systems at
different sites.
Use Wi-Fi hot spots generated from a hardwired router
as primary or backup network connection. Note that
this requires coordination with site host to avoid data
security and reliability issues of shared internet.
4
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Issues Proposed Solutions
Use EVSE network to create a Wi-Fi hot spot to allow
customers to connect their cellphones. The hot spot
can provide a backup option for a customer having
issues with their cellphone connection. A related option
is a mobile Wi-Fi connection, in which a portable device
uses a cellular network to create a hot spot.
Enable external antenna on EVSE for payment system
to increase signal reception. Antenna placement needs
to be thought out and addressed early in the design of
equipment.
Select card readers that offer multiple connectivity
options.
Network Hardware
Degradation of connectivity devices leads to
end of useful life of communications
equipment (e.g., modem, router).
Insufficient/inadequate communications
equipment preventative maintenance.
Establish a network component health check during
scheduled maintenance.
Network Integration
Poor software integration of the credit card
reader into the EVSE can affect overall
reliability and customers’ ability to use the
EVSE with their intended payment method.
Integrate credit card reader into EVSE network
connection, including network segregation via a
security switch.
d
Data Plan
Cellular data plan runs out of data.
Carefully select cellular data plan. Generally, select a
plan that does not run out of data but instead incurs
overage fees. Use data plans that are robust and do
not encounter reduced network speeds.
a
This refers to connectivity between the local card reader hardware (potentially through the EVSE modem to cloud
pod security policies backend) and payment merchant gateway (credit card payments facilitator); this does not refer
to merchant gateway cloud connection to CSO backend that releases charging to begin after payment is collected.
b
Unpublished research suggests ping time—how fast a response is received from an internet connection—is a better
indication of payment transaction success than upload and download speeds.
c
There is a concern for leased locations about the ability to use ethernet long term.
d
It is suggested that retrofits of this solution are complex, and data security requirements could make this
challenging.
5
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
3 Integration, Activation, and Installation
This section focuses on the integration and activation of the card reader payment system with the
EVSE.
Table 2. Integration, Activation, and Installation Issues and Proposed Solutions
Issues Proposed Solutions
Integration
EVSE and credit card system are not fully
integrated. EVSE and payment system
backends are not connected.
Integration of credit card reader into EVSE has
been challenging, largely due to software
issues.
Not all card readers are compatible with a
specific EVSE’s hardware and software.
Select card readers compatible with specific EVSE
models and that have received payment card
industry (PCI) certification or are PCI compliant.
Subject third-party integration of card reader and
EVSE to factory acceptance test and site
acceptance test.
The point-of-sale software should be tested with the
EVSE prior to deployment.
Card reader manufacturers and EVSE integrator
need to align software update schedules and
perform testing prior to deploying new card reader
software versions. Coordinate updates with all
parties, include release notes, and schedule for off-
peak hours. Implement automatic update checks.
Card readers integrated into EVSE outside of the
United States need to be registered for U.S.
systems prior to installation.
Activation & Installation
Incomplete activation of payment system prior
to installation.
Verify correct station location is assigned to card
reader during activation of payment system. This will
avoid confusion when troubleshooting and reduce
repair times.
During activation, make sure EVSE has correct
terminal ID connected to the correct merchant ID
provided by the acquirer.
Perform active monitoring to ensure proper
activation, installation, and ongoing operation.
a
Payment Standards
Noncompliance with PCI standards—
particularly for network segregation.
Comply with all PCI standards, including PCI data
security standards.
6
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Issues Proposed Solutions
Only use PCI-certified or PCI-compliant payment
solutions.
Use correct merchant category code: 5552 Electric
Car Charging.
Regularly audit and ensure compliance with PCI
data security standards. This requires a recurrent
certification once per year to stay aligned with the
latest PCI requirements.
a
This can be done via live monitoring or within the reconciliation process of transactions at the card reader level.
4 Robustness of Hardware
EV charging stations are generally not under a canopy, and card readers are subject to weather
impacts and incursions of dust, water, and other foreign debris.
Table 3. Robustness of Hardware Issues and Proposed Solutions
Issues Proposed Solutions
Hardware Physical Parameters
There has been limited scrutiny of robustness of
hardware.
Card readers are often outdoors and impacted
by dirt, dust, rain, ice, high/low temperatures,
and other climate impacts.
Operational specifications are for −20°C to
70°C; if these temperatures are exceeded, it
goes offline into safe mode.
Embed contactless/tap card reader into the EVSE.
Use weather-resistant card readers designed for
outdoor use.
Increase ruggedness of card reader hardware.
Card readers should meet International
Electrotechnical Commission ingress protection
rating of IP54 or IP66.
Card readers should meet the National Electrical
Manufacturers Association ratings of 4 or 4X.
Use card readers that shut down with high
temperatures and reactivate when a customer uses
the card reader.
Use card readers that send an alert to the backend
in the event of a disconnection or malfunction.
Conduct environmental tests for card reader
hardware.
7
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Issues Proposed Solutions
Design card readers to work in direct sunlight.
Similarly, design sites where EVSE faces away from
direct sunlight.
Vandalism
Card readers can be targets of vandalism and
tampering, causing malfunctions or security
issues.
Embed contactless/tap card reader into the EVSE.
Use tamper-evident seals, designs, surveillance
cameras, or other security measures.
Use impact protection IK-rated card readers for
resistance to impact.
Detect vandalism/tampering, send alert to backend,
and disable/shut down.
Hardware Integration
Externally integrated product selected by CSO
unlikely to go through validation that EVSE
manufacturers use for other components.
The selection and EVSE integration of the card
reader should consider methods and designs to
reduce the potential for environmental damage.
5 Customer Experience
The varied methods of payment and timing for authentication can confuse customers and lead to
payment challenges.
Table 4. Customer Experience Issues and Proposed Solutions
Issues Proposed Solutions
User Interface
The sequence of payment is not the same
at each charging station.
Customers are confused by multiple
payment options.
Customers lack familiarity with different
charging stations.
Card reader user prompts are difficult to
read or are not obvious because the
customer is looking at EVSE user interface
instead of card reader.
Display clear, step-by-step instructions at the charging
station.
Display card reader prompts on the EVSE’s user
interface.
Standardize the order of operations on the user
interface screen and in apps for payment for consistent
customer experience. The U.S. Payments Forum
published “Public Electric Vehicle Charging Terminal
Payment Flow Guidelines,” inclusive of suggested
payment prompts (U.S. Payments Forum 2023).
Educate customers on the various payment methods for
a charging session and provide easy-to-understand
instructions for each method.
8
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Issues Proposed Solutions
Quick-Response (QR) Code
The QR label has degraded and is not
readable.
Use more durable materials such as engraved stainless
steel or photo-anodized aluminum rather than stickers.
Static QR code should be displayed on card reader
screen and EVSE screen, rather than stickers.
Payment Declined
Customer credit or debit card declined.
Communicate that the credit or debit card is not
approved on the user interface the customer is
interacting with (kiosk screen, card reader, app, or
vehicle screen).
Receipts
Payment systems lack the means to
produce receipts.
The National Institute of Standards and Technology
Handbook 44 Section 3.40 provides a framework for
receipts, allowing for digital receipts delivered via text,
email, or as a web receipt.
Printed receipts are not recommended due to increased
maintenance.
Fleet Cards
Fleet cards may require answering prompts
on a screen prior to charging, and not all
card readers provide this capability.
Fleet cards are generally not
tap/contactless enabled.
Select card readers capable of meeting the
requirements for fleet card payment.
Work with fleet card providers on methods to enable
tap/contactless payment.
Accessibility
Accessibility of card reader.
The location/height of credit card reader must be
installed at or below 48 inches at an angle accessible
and convenient for all users and compliant with the
Americans with Disabilities Act. Note that this placement
may be outside the typical line of sight for nondisabled
customers, so also display card reader prompts on the
EVSE user interface.
9
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
6 Maintenance
Maintenance of payment hardware and systems may be overlooked and is an important
component of improving payment reliability.
Table 5. Maintenance Issues and Proposed Solutions
Issues Proposed Solutions
Regular wear and tear, as well as vandalism,
can cause card reader malfunction.
Payment system is generally not included in the
EVSE service and maintenance plan.
Plan and contract for timely support and repairs for
the payment systems, including regular cleaning of
swipe- and insert-style card readers.
Train staff to identify and report issues.
Test payment network strength with each
maintenance visit.
Maintain a small inventory of replacement parts.
Partner with card reader suppliers that offer prompt
support.
7 Other
Several other issues were introduced by task force members, including issues with RFID and
other more technical communication issues that involve payment issues.
Table 6. Other Issues and Proposed Solutions
Issues Proposed Solutions
NFC
When paying with NFC token (e.g., Apple Pay)
that is not set up properly, the payment is
rejected but the reason(s) why are not clear.
Push notifications or email are needed to resolve
issue.
There is not a single standard for RFID
implementation.
Industry could agree on a single RFID standard.
RFID
RFID tags can be issued that work on different
frequencies. Most card readers support only
one frequency.
Deploy RFID cards with the same frequency
throughout the industry. Alternatively, install more
expensive, dual-antenna RFID readers.
Roaming network impacts are experienced if
the RFID card identifier does not indicate to a
CSO which eMSP issued the card.
CSOs could use a hub for roaming that uses remote
start to mitigate any RFID card issues.
Plug & Charge
10
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Issues Proposed Solutions
Payment and user account are correct and
customer is using Plug & Charge but CSO
cannot authenticate.
No proposed solutions; more research is needed.
Plug & Charge Transport Layer Security (TLS)
loop failure where first vehicle fails for some
reason and this customer then authenticates
and pays via another method, and the EVSE
does not offer TLS; therefore, the next car
cannot ask for Plug & Charge.
No proposed solutions; more research is needed.
8 Conclusion
This document summarizes payment issues encountered by public EV charging infrastructure
and proposes solutions based on input from both individual ChargeX Consortium members in
one-on-one interviews and the ChargeX Consortium’s Payment & User Interface Task Force
collaborating as a whole. Key takeaways include the following:
• Because all forms of payment require network connectivity, special attention should be
given to charging station design to ensure a robust network connection. When relying on
a cellular network connection, employ an external antenna, redundant SIM card, and
carefully selected data plan. If using a local modem or router as a primary or backup
connection, a wired connection with ethernet cable routed through dedicated conduit is
superior to a Wi-Fi connection to a local modem or router. It is also important to have a
robust agreement in place with the site host to ensure data security and connection speed
are maintained. Regardless of the network connection method employed, it is important
to test network connectivity during the charging station design stage and repeat testing
during each maintenance visit. Finally, consider providing a Wi-Fi hot spot for customers
to ensure their cellular phones have connectivity for app- and phone-based payment.
• Credit card reader integration with the EVSE is critical for reliable operation. Use PCI-
compliant devices that are compatible with EVSE software. Test functionality after
device integration with the EVSE and point-of-sale software, both prior to and upon
installation. Plan for and coordinate card reader software update and verification
processes. Use merchant category code 5552—Electric Car Charging.
• Selecting a ruggedized card reader designed for outdoor use is also critical for reliable
operation. Test card readers to ensure robustness.
• Carefully design the EVSE user interface so that the customer understands how to use
multiple payment options and so that information presented on the credit card reader and
EVSE user interface is visible and consistent. Create a consistent user experience by
following “Public Electric Vehicle Charging Terminal Payment Flow Guidelines” (U.S.
Payments Forum 2023).
• Maintenance of payment systems is important for reliability and requires contracting to
ensure qualified staff conduct timely inspection and maintenance.
11
This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.
Future work is needed to quantify the benefits of these proposed solutions to help industry
prioritize solutions that realize the greatest improvement in payment system reliability.
References
U.S. Payments Forum. 2023. “Public Electric Vehicle Charging Terminal Payment Flow
Guidelines.” July 2023. www.uspaymentsforum.org/public-electric-vehicle-charging-terminal-
payment-flow-guidelines/.
U.S. Payments Forum. 2024. “Electric Vehicle (EV) Open Payments Working Committee.”
Accessed Feb. 8, 2024. www.uspaymentsforum.org/working-committees-sigs/electric-vehicle-
ev-open-payments/.
About the ChargeX Consortium
The National Charging Experience Consortium (ChargeX Consortium)
is a collaborative eort between Argonne National Laboratory,
Idaho National Laboratory, National Renewable Energy Laboratory,
electric vehicle charging industry experts, consumer advocates,
and other stakeholders. Funded by the Joint Oce of Energy and
Transportation, the ChargeX Consortium’s mission is to work together
to measure and signicantly improve public charging reliability and
usability by June 2025. For more information, visit chargex.inl.gov.
NREL/TP-5400-88821 • February 2024
