Yesterday I argued that electric cars are still only about 4% of the vehicles on European roads, even though they are 20% of new sales.

Here is why that number should worry anyone building charging infrastructure.

At 4% of the fleet, the drivers without a home charger are a rounding error. Most early EV owners have a driveway, a wallbox, a garage. The charging problem looks solved because the people who have it are invisible.

But watch what happens as the fleet share climbs from 4% toward 10, 15, 20%. The next wave of buyers is not the homeowner with off-street parking. It is the person in a city apartment. The family renting with no garage. The people for whom "just charge overnight at home" was never an option.

We have spent a decade building charging for the journey - the motorway, the holiday drive, the long trip. That problem is largely solved. We have barely begun building charging for the street where people actually live.

And the timing is unforgiving. The urban-charging gap does not grow gently. It arrives exactly as the fleet crosses into double digits - which, on current trends, is this decade.

The motorway is solved. The city is not. That is where the next phase of this transition will be won or lost, and we are not building fast enough.