You plug in at a motorway service station and the screen says 80p/kWh. For a second, your whole EV business case flashes before your eyes.
That reaction makes sense; it's also the reason most fleets are watching the wrong number.
One session tells you almost nothing
An 80p/kWh rapid charge looks alarming on its own, but that same driver might spend the rest of the month charging at home on a smart tariff for 7p/kWh. Look at the month as a whole and that picture can change drastically.
The issue isn't that public charging costs more because it often does. The issue is judging your fleet's EV costs one session at a time. It's the same as panicking about your fuel budget because you filled up at the one garage on the motorway that charges more than everywhere else.
Meet your new financial north star: average unit rate
Average unit rate is the cost per kWh across every session and every driver in your fleet, blended together. Not the cheapest session. Not the one that stung. The real, weighted average of what you're paying to keep your fleet moving.
It matters because it reflects reality. A fleet with a high share of home charging and occasional public top-ups might have an average unit rate of 15-20p/kWh, even if a handful of individual sessions look expensive on their own. Judge that fleet by its worst session and you'll make bad decisions. Judge it by its average unit rate and you'll see the business case much more clearly.
Why this matters now
Across 2025, public charging made up just over a quarter of all sessions on our platform; it accounted for more than half of total spend. That gap is why session-level thinking misleads fleet managers. A small share of sessions does most of the damage to the budget, while home charging quietly does the heavy lifting and gets overlooked.
If you're only looking at public charging invoices, you're seeing the most expensive slice of your costs and mistaking it for the whole picture.
How to work out your fleet's average unit rate
- Add up total spend. Combine home charging reimbursements with public charging invoices and card spend.
- Add up total kWh delivered. Include every session between home, depot and public.
- Divide total spend by total kWh. That's your average unit rate.
The maths is simple; the hard part is getting visibility over home charging spend in the first place. Home charging is usually the cheapest part of the mix, but it's also the part fleet managers have had the least visibility over, buried in individual drivers' home energy bills rather than sitting on one invoice.
The mistake to avoid
The biggest mistake fleets make when switching to EV is treating charging as an afterthought; rolling out vehicles without building visibility into where drivers charge and what they pay. Without that data, the savings home charging offers are there, but out of reach.
Fleets that get this right treat charging like fuel. One charge card and one bill with full visibility over where every driver charges and what it costs, at home and on the road.
Bringing your average unit rate down
Once you're tracking it, the approach is simple. Push as much charging toward home as you reasonably can and make the public charging that does happen as cheap as possible. Making that easy for drivers and giving fleet managers the data to check it's working, is where the real work sits.
Want to know your fleet's average unit rate? Get in touch with the Rightcharge team to see how it stacks up, and where the biggest savings are hiding.