4G and 5G Cellular Connectivity for EV Charge Points

Cellular Connectivity for EV Charge Points: The Complete Guide

Every networked EV charge point needs a reliable connection to a Charging Station Management System (CSMS). Without it, the charger cannot authenticate users, start or stop sessions, report energy consumption, process payments, or receive remote commands. In the majority of commercial EV charging deployments – car parks, forecourts, retail sites, fleet depots, kerbside installations, and motorway service areas – there is no existing broadband infrastructure. Cellular 4G or 5G is the practical, cost-effective answer.

This guide covers everything installers, charge point operators (CPOs), and system integrators need to know: how OCPP connectivity works over cellular, which SIM card to use, which router to specify, how to choose and position the antenna, and how to resolve the connectivity problems that appear most often in the field.

How OCPP Uses the Cellular Connection

OCPP (Open Charge Point Protocol) is the open standard for communication between EV chargers and a CSMS. Current deployments primarily use OCPP 1.6, with OCPP 2.0.1 adopted by newer platforms. Both versions use a WebSocket connection – a persistent, bidirectional TCP connection that the charger initiates to a URL provided by the CSMS operator.

Because OCPP uses an outbound WebSocket, the charger initiates the connection to the cloud. The CSMS does not need to reach inbound to the charger’s IP address. This has a direct implication for SIM selection: a standard dynamic IP SIM is sufficient for most cloud-hosted CSMS platforms, because the connection flows outward from the charger to the cloud, not the other way around.

The exceptions are deployments where the CSMS is hosted on a private server, where the operator runs a VPN between chargers and the management backend, or where the CSMS security policy requires the charger to connect from a known, whitelisted IP address. In those cases, a fixed IP SIM card is required.

OCPP Data Consumption – What to Expect

OCPP is lightweight. A Heartbeat message with its acknowledgement is under 1 KB. A complete charging transaction generates between 2 and 10 KB of OCPP data depending on the metering interval and session duration. A moderately busy commercial charger with 10-15 sessions per day and 30-second metering intervals uses approximately 30-80 MB of cellular data per month. A charger with longer average session times and 60-second meter reporting may use as little as 15 MB per month. Firmware updates over the air are the largest single data events, typically 5-20 MB per update.

A 500 MB monthly SIM allowance is adequate for a single charger in most deployments. A hub router serving four to eight chargers on one site, combined with occasional firmware updates and RMS management traffic, fits comfortably within 1-2 GB per month.

What Happens When the Connection Drops

Understanding the consequences of a dropped OCPP connection is important when specifying connectivity, because it defines the resilience requirements for the installation.

Most chargers enter a degraded operating mode when the OCPP connection is lost. Depending on the charger and CSMS configuration, behaviour varies:

• Chargers configured for offline authorisation continue to allow charging using locally cached RFID tokens. Sessions are stored locally and synchronised to the CSMS when the connection is restored.
• Chargers without offline authorisation configured stop accepting new sessions. A charger that shows “Unavailable” or “Offline” to a driver is a direct revenue and reputational loss for the CPO.
• Remote commands – stop session, change availability, reset – cannot be executed while offline.
• Meter values are not reported in real time. Billing accuracy depends on session data stored locally and uploaded on reconnection.
• Payment processing via the CSMS fails if the operator uses back-end payment authorisation rather than RFID cache.

For high-footfall commercial deployments, continuous connectivity is not optional. Dual SIM routers with automatic failover to a second network ensure that a single network outage does not take the charger offline.

Choosing the Right SIM for an EV Charge Point

Standard Data SIM

A standard IoT data SIM on any UK network is sufficient for charge points connecting to a cloud-hosted CSMS over a standard WebSocket URL. The charger initiates the outbound connection, the cloud CSMS has a fixed DNS address, and no inbound connection to the SIM is required. Data consumption is low, so any data plan from 500 MB upward covers a single charger comfortably.

Fixed IP SIM

A fixed IP SIM card assigns a permanent, static public IP address to the router’s WAN interface. This is required in four specific scenarios:

• The CSMS is hosted on a private server and the operator has configured an IP whitelist that only accepts connections from known addresses.
• The operator runs an IPsec or OpenVPN tunnel between the router and the backend, and the VPN configuration references the SIM’s IP address.
• A payment terminal or ANPR camera at the site needs to connect back to the charger’s local network. This requires inbound routing to the SIM’s IP, which only works with a fixed IP.
• Remote access to the router’s WebUI or to devices on the charger’s LAN is required without using a cloud-based remote management platform.

Multi-Network Roaming SIM

For sites where single-network coverage is poor or unreliable – rural locations, underground car parks, kerbside installations in signal-challenged areas – a roaming SIM that can switch between all UK networks provides a significant resilience improvement over a single-network SIM. See our roaming SIM cards for details.

Private APN

Large CPO networks deploying dozens or hundreds of charge points sometimes use a private APN (Access Point Name) that connects all their SIMs to a dedicated private network rather than the public internet. This provides network-level isolation, centralised traffic monitoring, and removes the charger’s OCPP connection from the public internet entirely. Private APN configurations are arranged directly with the SIM supplier. Contact routerstore.com on 0300 124 6181 to discuss private APN options for larger EV deployments.

Choosing the Right Router

Router selection for EV charge point deployments depends on three factors: how many chargers the router serves, whether RS485 serial interfaces are needed for smart meter or load management integration, and the bandwidth requirement of the site.

Single Charger at a Simple Site

A single charge point with OCPP over cellular needs only a compact industrial router with a single SIM and basic firewall functionality. The Teltonika RUT241 is the minimum viable specification: single 4G Cat 4 connection, eSIM support, dual-band Wi-Fi, and full RutOS with VPN capability. For sites where dual SIM failover is required, the RUT901 or RUT951 add a second SIM slot.

Single Charger with RS485 Smart Meter

Many charge points require integration with an RS485 energy meter for dynamic load management or billing metering. If the router is handling both the OCPP cellular backhaul and the Modbus RS485 meter connection, an RS485-equipped model is required. The RUT956 and TRB145 both provide RS485 with full Modbus and MQTT support, allowing meter data to be forwarded alongside OCPP traffic.

Multiple Chargers on One Site

A hub router serving multiple charge points via Ethernet switch or Wi-Fi needs enough Ethernet ports and processing capacity to handle simultaneous OCPP sessions without packet loss. The RUTX11 (4x Gigabit Ethernet, dual SIM, 4G Cat 6) is the most common choice for multi-charger sites of four to eight units. For sites with higher throughput requirements or where future 5G upgrade is anticipated, the RUTX50 or RUTM series provide the headroom.

High-Footfall Commercial and Motorway Sites

Motorway service area chargers, large retail park installations, and fleet depot hubs may run 10-30+ charge points simultaneously and serve additional services such as ANPR cameras, CCTV, payment terminals, and network management systems. A 5G router with dual SIM failover and multiple Gigabit Ethernet ports is appropriate here. The RUTM52 (dual 5G modems, load balancing) or RUTX50 (5G, 5x Gigabit Ethernet) serve these deployments. Dual SIM active-active load balancing distributes traffic across two network connections, providing both resilience and higher aggregate throughput.

Antennas for EV Charge Point Installations

The router’s internal antennas are adequate for installations where the router is mounted in an outdoor cabinet or enclosure with line-of-sight cellular coverage. Most car park, forecourt, and roadside charger locations fall into this category. External antennas are required when:

• The router is installed inside a metal enclosure that attenuates cellular signals.
• The installation is in an underground car park, basement, or enclosed structure.
• The site is in a rural or semi-rural location where signal strength at ground level is marginal.
• Signal strength is adequate but variable, causing intermittent disconnections that cause OCPP heartbeat timeouts.

Standard Omni Antenna for Outdoor Enclosures

A 4G omni antenna with SMA connector, mounted on top of or adjacent to the charge point enclosure, is the most common external antenna configuration. Standard gain of 3-5 dBi provides measurable improvement over internal antennas in an enclosure. MIMO configurations (two antennas for 2×2 MIMO, four for 4×4) improve data throughput and connection stability on Cat 6 and higher modems, which matters when multiple chargers share one router.

High-Gain Antenna for Rural and Poor-Signal Sites

At rural locations with weak base station signal, a high-gain directional antenna (9-12 dBi) pointed toward the nearest base station can recover a connection that would otherwise be too marginal for reliable OCPP operation. The antenna is mounted externally on a mast or building surface. A Fullband or Poynting high-gain 4G antenna connected via a low-loss coaxial cable run to the router inside the enclosure is the standard approach for these sites.

Combination 4G + 5G MIMO Antenna

For 5G routers serving large sites, a MIMO antenna covering both 4G and 5G bands in a single enclosure reduces the number of antenna cable penetrations required in the enclosure. These are available in puck, panel, and colinear form factors from the Fullband range stocked at routerstore.com.

Placement Principles for EV Charge Point Antennas

• Mount the antenna on the exterior of the enclosure or on the charge point housing itself, not inside a metal cabinet.
• Height improves signal – a rooftop or top-of-charger-column mount outperforms a ground-level cabinet mount at the same location.
• Underground car park installations almost always require an antenna run to the surface, or a repeater/DAS system for the whole structure. A coaxial cable run of up to 10 metres with a low-loss cable and LNA-equipped antenna maintains acceptable signal levels.
• Avoid mounting directly adjacent to high-power electrical cables. EMI from EV charging cables (particularly DC fast chargers) can degrade cellular signal if the antenna is within 0.5 m of high-current conductors.
• For MIMO routers, use two antennas at least 0.5 m apart for meaningful MIMO gain.

Remote Management and VPN

A cellular router at an EV charge point is itself a piece of critical infrastructure that needs to be monitored and managed remotely. Router reboots, APN changes, firmware updates, and firewall rule changes should all be possible without a site visit.

Teltonika’s Remote Management System (RMS) provides a cloud dashboard showing connection status, signal strength, data usage, and uptime for every router in a fleet. Remote access to the router WebUI is available via RMS without requiring a fixed IP SIM. This is the recommended management approach for CPOs deploying multiple sites. See our Teltonika RMS guide for details.

For operators who require a VPN between the router and their backend – for example, to carry OCPP over a private network rather than the public internet – Teltonika routers support OpenVPN, IPsec, WireGuard, and L2TP. A fixed IP SIM card is required for the VPN termination point. See our VPN on cellular routers guide for configuration detail.

Common Connectivity Problems and Solutions

The following issues appear repeatedly in EV charging installations using cellular routers. Each has a specific cause and a known resolution.

OCPP charger shows Offline or Unavailable despite the router being connected

This is the most common reported problem. The router has cellular connectivity but the charger’s OCPP WebSocket connection to the CSMS has failed or timed out. Check that the CSMS URL and Charge Point ID entered in the charger configuration are correct. Verify that the router is not blocking outbound WebSocket traffic on the port used (typically 80, 443, or 8080). Check the router firewall settings and confirm no outbound connection restriction is in place. If the CSMS uses a whitelist, confirm the SIM’s current IP address is on the list – or switch to a fixed IP SIM so the address never changes. If the charger lost connection and has exceeded its reconnection attempt limit, a full power cycle of the charger (not just a soft reset) is often required.

OCPP connection drops after 30-60 minutes and does not recover automatically

This is typically caused by a NAT timeout on the network. The router’s cellular connection uses NAT to translate the SIM’s private IP address to a public IP. If no traffic passes through the NAT table for longer than the carrier’s NAT timeout period (often 30-60 minutes on inactive connections), the session is dropped. The OCPP heartbeat interval should be set shorter than the carrier’s NAT timeout – 60 seconds or less is recommended. If the CSMS allows configuration of the heartbeat interval, reduce it to 30 seconds for cellular deployments.

Connection refused when a payment terminal or ANPR camera tries to connect to the charger

When a device on the same LAN as the charger tries to connect to a fixed local IP address on the charger’s network, and connection is refused, this is almost always a NAT or DHCP configuration issue. The charger expects the terminal at a specific IP (e.g. 192.168.111.50) but the router’s DHCP is assigning a different address, or a firewall rule is blocking the traffic. Assign the terminal a static DHCP lease matching the expected IP in the router’s LAN configuration. If the terminal needs to be reachable from outside the LAN via the cellular WAN, a fixed IP SIM and a static NAT (port forwarding) rule are required.

Router log shows Mobile network rejection repeatedly

This message appears when the SIM is failing to register on the cellular network. The most common causes are: incorrect APN settings for the SIM in use; SIM not activated or data bundle exhausted; SIM inserted in the wrong slot on a dual-SIM router where the active SIM profile is set to SIM 2; network band mismatch (the router is configured to lock to a specific band not available at this location). Check the APN setting matches the SIM supplier’s documentation exactly. Check the SIM is active and has available data. Remove the band lock if one has been applied and allow auto band selection.

Signal adequate but connection drops during charging sessions

Intermittent signal problems during active EV charging may be caused by electromagnetic interference from the charger’s power electronics affecting the router’s cellular antenna if mounted in close proximity. Check signal quality (RSRP and RSRQ values, not just signal bars) in the router WebUI. RSRP below -100 dBm is marginal for sustained OCPP operation. If RSRP is adequate but RSRQ is poor (below -12 dB), the signal environment is noisy and an external antenna in a different location will help. Move the external antenna away from the charge point’s power cable and inverter.

EV Charging Connectivity Glossary

OCPP (Open Charge Point Protocol)

The open standard for communication between EV charge points and a Charging Station Management System. OCPP 1.6 is the current widespread standard. OCPP 2.0.1 is the modern replacement, adding enhanced security, device management, and smart charging features. The two versions are not backwards compatible.

CSMS (Charging Station Management System)

The backend software platform that manages a network of charge points. Also called the Central System in OCPP 1.6 terminology. Examples include ChargePoint, EVBox Everon, Monta, Eaton Green Motion, and self-hosted platforms such as SteVe. The CSMS provides remote monitoring, user authentication, billing, and session management.

WebSocket

The network protocol used by OCPP for communication. A WebSocket is a persistent, bidirectional TCP connection. The charger opens the WebSocket to the CSMS URL and keeps it open. Unlike HTTP, which opens and closes a connection for each request, the WebSocket stays alive continuously, allowing the CSMS to send commands to the charger at any time without the charger polling. Most OCPP WebSocket connections use the encrypted wss:// prefix (WebSocket Secure over TLS).

APN (Access Point Name)

The identifier that tells the SIM which data network to connect through. Each mobile network operator has one or more APNs. For standard internet access, the default APN for the network is used (e.g. internet for EE, or wholesale for MVNOs). For private APN deployments, the APN routes traffic to a dedicated private network rather than the public internet. Incorrect APN settings are the most common cause of a router failing to obtain a cellular data connection.

Fixed IP SIM

A SIM card that always presents the same static public IP address on the cellular WAN. Standard SIMs receive a dynamic IP that changes on each reconnection. A fixed IP allows the CSMS or VPN server to know the charger’s address in advance, enables IP whitelisting, and supports inbound connections from remote systems.

Dual SIM failover

A router feature where a second SIM on a different network takes over the WAN connection automatically if the primary SIM loses connectivity. The failover time is typically under 30 seconds on Teltonika routers, which is below most OCPP heartbeat timeout thresholds. Dual SIM failover eliminates single-network outage as a cause of charger downtime.

RSRP (Reference Signal Received Power)

The key cellular signal quality measurement in LTE (4G) networks. RSRP is measured in dBm. Values above -80 dBm are excellent. Values between -80 and -100 dBm are good. Values between -100 and -110 dBm are fair and may cause occasional disconnections. Values below -110 dBm are poor and an external antenna should be used. This is more meaningful than the signal bar display, which varies by manufacturer and often masks poor signal conditions.

RSRQ (Reference Signal Received Quality)

A measure of signal quality taking interference into account, independent of signal strength. RSRQ values above -9 dB are good. Values below -12 dB indicate significant interference or congestion even if RSRP appears adequate. Poor RSRQ causes dropped packets and unstable TCP connections, which directly affects OCPP WebSocket stability.

NAT timeout

Mobile network operators maintain a NAT (Network Address Translation) table that maps the SIM’s private IP to a public IP. If no traffic flows through a NAT session for a carrier-defined idle period (typically 30-600 seconds), the session is dropped and any open TCP connections through it are terminated. OCPP connections dropped by NAT timeout appear as sudden charger disconnections at regular intervals. The solution is to set the OCPP heartbeat interval below the carrier’s NAT timeout period.

VPN (Virtual Private Network)

An encrypted tunnel between the router and a remote server. For EV charge point deployments, VPN is used to carry OCPP traffic over a private network rather than the public internet, to provide secure remote access to the charger’s local network, or to connect all sites in a CPO network to a central management system. Teltonika routers support OpenVPN, IPsec, WireGuard, and L2TP.

Dynamic Load Management (DLM)

A function that limits the total power drawn by a group of charge points to stay within the site’s available electrical capacity. DLM requires real-time communication between the charge points and either a local controller or the CSMS. If the OCPP connection drops during DLM operation, chargers may default to their maximum power draw, risking a site overcurrent trip.

CPO (Charge Point Operator)

The organisation that owns and operates a network of EV charge points. The CPO is responsible for the hardware, connectivity, maintenance, and user experience of the charging network. CPOs are the primary customers for cellular router and SIM connectivity solutions in the EV charging sector.

OCPP Heartbeat

A periodic message sent by the charge point to the CSMS to confirm the connection is alive. The heartbeat interval is configured in the CSMS and is typically between 30 and 300 seconds. If the CSMS does not receive a heartbeat within the configured interval, it marks the charger as offline. On cellular connections, a 30-60 second heartbeat interval is recommended to prevent NAT timeout causing false offline status.

Related Products and Further Reading

For SIM connectivity, see our IoT SIM connectivity hub, including fixed IP SIM cards for VPN and whitelisted CSMS connections and multi-network roaming SIM cards for sites with variable coverage. For router selection, browse the Teltonika 4G router range and the Teltonika 5G router range. For RS485 smart meter integration alongside OCPP, see the Teltonika TRB series IoT gateways. For remote monitoring and management of your router fleet, see the Teltonika RMS guide. For VPN configuration on cellular routers, see our VPN on cellular routers guide.