What is the difference between steered and unsteered roaming for an EV charger?

Steered roaming forces the SIM to try a preferred carrier first —even if its signal is weak at the charger location. Unsteered roaming connects to whichever carrier has the strongest signal. For fixed infrastructure like EV chargers, unsteered is the correct choice: the SIM should prioritize RF reality at the specific installation point, not a commercial agreement made at procurement time.

Does an EV charger SIM need a static IP?

Not for basic OCPP operation —the charger initiates connections to the CPMS, which works through carrier-grade NAT. But if the CPMS needs to reach the charger (remote commands, firmware updates), the charger must be reachable via static private IP and IPsec VPN tunnel. Most managed charger fleets over 50 units deploy private APN with VPN to the CPMS cloud.

Why is SGP.32 eSIM better than a physical SIM for EV chargers?

EV chargers are stationary and have 10+ year deployment lifecycles. During that time, carrier coverage at the site will change, carriers may enter or exit markets, and the operator may want to switch providers. With a physical SIM, any carrier change means a site visit. With SGP.32 eSIM, the new profile is loaded over-the-air through the eIM —no truck roll. For fleets over 100 chargers, this alone justifies the eSIM hardware cost.

EV-Ladesaulen: 1 von 4 offline

June 3, 2026 · 8 min read · Case Studies

>50% Netzprobleme. Multi-Netz-SIM.

TL;DR: The #1 cause of failed EV charging sessions is not the charger hardware —it is network connectivity failure. Industry data shows over 50% of failed sessions trace to network issues, and roughly 1 in 4 public chargers is non-functional at any given time. The root cause in most cases: a single-network SIM installed in a charger at a location where that specific carrier has weak or no coverage. In approximately 15% of Germany, only one MNO has usable 4G. If the charger has a different MNO's SIM, it will not connect —permanently. Multi-network SIMs with unsteered roaming solve this by connecting to the strongest available network at the specific installation point. eSIM with policy-driven failover (SGP.32) adds the ability to load new carrier profiles when coverage changes —without a site visit.

Why EV Chargers Are a Uniquely Difficult Connectivity Problem

An EV charger is a stationary device —it cannot move to find better signal. It is often installed in underground parking garages (concrete and steel attenuation: 20-30 dB), rural highway rest stops (single-carrier coverage at best), or urban locations where the nearest tower is congested during peak charging hours (6-9 PM). The SIM that was provisioned at the factory has no knowledge of the installation site's RF environment.

This is fundamentally different from a mobile IoT device (vehicle tracker, asset tag) that can drive to better coverage. The charger is bolted to the floor. The SIM must adapt to the location —not the other way around.

OCPP (Open Charge Point Protocol), the industry-standard communication protocol between chargers and central management systems, runs over WebSocket or SOAP/XML. It requires a persistent or frequently re-established IP connection. If the cellular link drops for more than the OCPP heartbeat interval (typically 30-60 seconds), the charger appears offline to the CPMS (Charge Point Management System) —even if it is capable of delivering power. A driver arrives, sees no available charger in the app, and drives away. The charger was never broken. The SIM was just on the wrong network.

Source: KORE Wireless, "Reliable and Scalable Global Connectivity for EV Charging Starts with KORE Super SIM", June 2025. Available at https://www.korewireless.com/blog/reliable-and-scalable-global-connectivity-for-ev-charging-starts-with-kore-super-sim/

Steered vs Unsteered Roaming: The Technical Distinction That Determines Uptime

Most consumer SIMs and many IoT SIMs use steered roaming: the SIM always attempts to connect to a preferred carrier first, even if that carrier's signal at the installation site is weak or absent. This works for mobile devices that move through varying coverage —on average, the preferred carrier is the best choice. For a stationary EV charger at a specific GPS coordinate, "on average" is irrelevant. What matters is which carrier has the strongest signal at that exact location.

Unsteered (non-steered) roaming: the SIM scans all available networks and connects to the one with the strongest signal —regardless of commercial preference. For fixed infrastructure, this is the correct approach. The SIM should prioritize RF reality over commercial hierarchy.

In approximately 15% of German territory, only one carrier has usable 4G. In about 2%, no single carrier has usable 4G, but the combination of all three (Deutsche Telekom, Vodafone, Telefónica) provides coverage across the territory. A multi-network unsteered SIM installed in those 2% of locations works —every single-network SIM fails.

Source: Wevolver, "M2M SIMs for E-Charging Stations: Reliable and Secure Connectivity for Charging Stations Worldwide", January 2026. Available at https://www.wevolver.com/article/m2m-sims-for-e-charging-stations-reliable-and-secure-connectivity-for-charging-stations-worldwide

OCPP Over Cellular: What the Protocol Needs From the SIM

OCPP 1.6-J and 2.0.1 —the dominant versions deployed in 2026 —require:

1. Persistent or frequently re-established TCP connection: OCPP over WebSocket maintains a long-lived connection. If the cellular network silently drops the TCP session (common with carrier-grade NAT timeouts of 60-120 seconds), the charger must re-establish it before the next heartbeat interval. The SIM must support always-on APN configuration —not on-demand PDP context activation.

2. Outbound-initiated connections: standard OCPP architecture has the charger (client) connecting to the CPMS (server). This works with carrier-grade NAT —the charger initiates the connection. But if the CPMS needs to reach the charger for firmware updates or remote commands, the charger must be reachable —which requires a static private IP or a VPN tunnel. A private APN with IPsec VPN to the CPMS cloud is the standard architecture for managed charger fleets.

3. TLS encryption: OCPP 2.0.1 mandates TLS 1.2 or higher for all communication. The SIM's data path must support TLS without interference —some low-cost IoT SIMs route traffic through proxies that break TLS certificate validation. Verify that the SIM provides transparent IP access.

Source: Transatel, "How IoT Connectivity Cuts Costs and Enables EV Energy Management", February 2026. Available at https://www.transatel.com/news-and-insights/blog/enable-ev-energy-management/

SGP.32 for EV Chargers: Why eSIM Is Entering Charger Procurement Specs in 2026

EV charger procurement is shifting toward SGP.32 eSIM for three reasons that are specific to fixed infrastructure:

1. Carrier coverage changes: a charger installed in 2024 on Vodafone DE may be in a location where Deutsche Telekom deploys a new tower in 2026 —improving coverage from -105 dBm to -78 dBm. With a physical SIM, switching carriers means a truck roll. With SGP.32 eSIM, the eIM pushes the DT profile over-the-air. The charger switches. No site visit.

2. Market exit risk: regional carriers and MVNOs enter and exit markets. If the carrier providing connectivity to 500 chargers exits the market, those chargers have no connectivity until every SIM is physically replaced. With eSIM, the replacement profile is loaded remotely.

3. Private network integration: large fleet operators and utilities are deploying private LTE/5G networks at depot and highway charging hubs. An SGP.32 eSIM can carry both a public MNO profile (for on-road chargers) and a private network profile (for depot chargers) on the same physical chip —switching based on location policy.

Source: Kigen, "5 Ways eSIMs Accelerate Grid Modernization for C&I Utilities", November 2025. Available at https://kigen.com/resources/blog/5-ways-esims-accelerate-grid-modernization-for-ci-utilities/

The Cyber Security Dimension: Why Some Chargers Should Not Be on the Internet

An alternative architecture proposed by HeyCharge (May 2026) challenges the assumption that every EV charger needs persistent cellular connectivity. For security-sensitive sites —military bases, critical infrastructure, corporate campuses —a charger with no internet connection eliminates the entire remote attack surface. Authentication happens locally via BLE (driver's phone), session data is stored and forwarded through the driver's phone as a courier. The charger itself never connects to any network.

This is not a replacement for cellular-connected chargers —it is a design option for sites where the security risk of internet-connected infrastructure outweighs the operational convenience of remote management. The trade-off: no real-time monitoring, no remote firmware updates, asynchronous billing.

Source: HeyCharge, "EV Charging That Doesn't Touch Your Network: The Cybersecurity Case for Offline-First Architecture", May 2026. Available at https://www.heycharge.com/news/ev-charging-without-network-access/

Choosing the Right SIM Architecture for EV Charger Deployment

Scenario	SIM Type	Why
----------	----------	-----
Single urban charger, known-good coverage	Unsteered multi-network SIM	Simplest; works if any carrier is strong at site
Highway rest stop, unknown coverage	Unsteered multi-network SIM + site survey with AT+CSQ before install	Validate signal before bolting charger to pad
Multi-country fleet (100+ chargers)	Multi-IMSI eSIM + private APN + IPsec VPN to CPMS	Manageable from single CMP; local breakout per country
Depot + on-road mix	SGP.32 eSIM with public + private network profiles	Public profile for highway chargers; private profile for depot
High-security government/critical infra	Offline-first BLE, no SIM	Eliminates remote attack surface