A charger in a basement car park with one bar of signal will work in commissioning, when a technician stands next to it with the door open, and fail intermittently for the next three years. Connectivity is the least glamorous part of a charging deployment and one of the largest contributors to unavailability.
Specify it at survey, not at install
Signal strength at the exact mounting position, with the enclosure closed, measured during the site survey. Not at the entrance, not on the surveyor’s phone held at head height. Basements, lift lobbies and metal-clad structures routinely lose enough signal to make a marginal connection unusable.
- Where signal is marginal, an external antenna is cheap and usually sufficient.
- Where it is absent, wired ethernet from the building’s network is the answer, and it needs to be in the civil scope before the trench is closed.
- Where the host offers wifi, take it as a secondary path, never as the primary. Building wifi changes passwords and nobody tells you.
Choosing the SIM
| Option | Good for | Watch out for |
|---|---|---|
| Consumer prepaid SIM | A first site, quickly | Expiry, recharge failures, no fleet visibility |
| M2M single-network plan | Sites with known good coverage | One network, one coverage hole |
| Multi-network / roaming M2M | Anything at scale | Higher unit cost, worth it |
| Wired ethernet | Basements, malls, offices | Depends on the host’s network staying up |
Multi-network M2M is the answer for most deployments. The unit cost is higher and the failure mode it removes — one operator having a bad month in one city — is exactly the one that takes a site offline for a week.
Monitor the connection, not just the charger
The heartbeat tells you the charger is reachable. It does not tell you the connection is degrading. Two additional signals separate a network problem from a hardware one:
- 01Reconnection frequency. A charger that reconnects forty times a day is on a failing link, even though it is online every time you look.
- 02Heartbeat interval drift and message latency. Rising round-trip times precede an outage by days, which is enough warning to act.
Both are cheap to record and neither is usually surfaced. An operator who watches them stops dispatching technicians to chargers that were never broken.