Connectivity is the part of charger design most often validated in the wrong environment. It works on the bench, it works in the office, and it fails in an underground car park behind a concrete column inside a metal enclosure.
That environment is not the exception. For a large share of deployed AC chargers it is the normal case.
What each bearer is actually good for
Most deployments end up with more than one, because the failure modes are uncorrelated. A site whose Wi-Fi is down usually still has cellular coverage, and vice versa.
- Wi-Fi: cheap, depends on infrastructure you do not control, and on credentials that change without anyone telling you.
- Cellular: independent of site infrastructure, carries a recurring cost per unit, and coverage underground is frequently poor.
- Ethernet: the most reliable by a wide margin, and requires cable to each unit, which is a civil cost.
- Bluetooth: not a backhaul. Useful for commissioning and local interaction when the backhaul is down.
The enclosure is part of the antenna system
A metal enclosure attenuates radio signals, and where the antenna sits relative to it determines how much. An antenna placed for mechanical convenience, on the wrong side of a ground plane or against a metal panel, can lose a great deal of the link budget before the signal leaves the box.
This is why connectivity is a mechanical design consideration rather than a module selection. Changing an enclosure material or layout during localization can degrade connectivity without anyone associating the two.
Test where it will live
Bench validation establishes that the module works. It says nothing about whether the product will connect from the far corner of a basement car park, which is the question that matters.
Representative testing means an installed unit in a genuinely difficult location, measuring signal quality over time rather than at one moment, because these environments vary with occupancy, vehicles and weather.
Credential management is an operational cost
Wi-Fi credentials change. A site that rotates its network password disconnects every charger on it, and if the only way to update them is a physical visit with a laptop, that becomes an expensive recurring event.
Local commissioning over Bluetooth exists largely to solve this. It lets an engineer, or in some models the site owner, restore connectivity without opening the unit or bringing specialist equipment.
Behaviour when the connection is gone
This is a product decision that is frequently left to whatever the firmware happened to do. A charger that refuses to work offline turns a network problem into a service outage. A charger that works offline and forgets loses revenue.
The reasonable position is offline operation with local authorisation and stored transactions, reconciled on reconnect. That requires design, storage and a reconciliation path, and it should be specified rather than discovered.
Reconnection behaviour matters as much as connection
Networks recover. A charger that does not retry, or retries aggressively enough to be a problem, or reconnects but does not resynchronise its state, turns a brief outage into a lasting one.
Backoff strategy, state resynchronisation and clean handling of a backend that returns before or after the charger does are all part of connectivity design, and all of them are visible only in field conditions.
Cost at fleet scale
A cellular subscription per charger is a small number that becomes a large one across a fleet, and it recurs for the life of the asset. That cost belongs in the total cost model from the start rather than appearing as an operational surprise.
It is also an argument for Ethernet where the civil work is happening anyway, since the marginal cost of cable during a trench is far lower than retrofitting it later.