How do EV battery sizes and charging curves affect your site?

Match your chargers to the energy drivers need during their visit, rather than the battery's headline capacity. Network Rail describes how vehicle capability and charging equipment constrain delivery [S1]. In an assumed 60 kWh battery, moving from 20% to 80% adds 36 kWh before losses. Average power determines how quickly that happens. Checked October 2026.

Last checked 16 October 2026

Why does average charging power matter more than the peak?

Your site sells a useful charging stop, not a momentary power reading. A charger can have spare power while the vehicle accepts less. Network Rail’s infrastructure guide distinguishes the equipment’s capability from what the vehicle can receive. Use that distinction when deciding whether a higher-rated unit fits your visitors. [S1]

Define the units before comparing proposals. A kilowatt (kW) measures power: how quickly energy is transferred. A kilowatt-hour (kWh) measures energy. Battery capacity and energy sold belong in kWh; the rate at which you deliver that energy belongs in kW. See kW versus kWh. [S1]

Ask a bidder for expected energy delivered during a representative visit. A peak rating alone does not answer that question. Request the assumed vehicle capability, arrival charge, available site power and session length alongside the result. Keep those assumptions identical when comparing equipment.

How much energy does a visitor actually need?

Start with the difference between arrival charge and departure target. For the following calculation, assume a usable battery capacity of 60 kWh. This is an illustration, not a statement about the average UK vehicle.

These are battery-side calculations before losses. Do not treat them as identical to electricity bought through your site meter or electricity billed at the chargepoint. Define each measurement boundary in the proposal. [S1]

For a fleet, collect vehicle specifications and departure needs. For customer parking, ask visitors what would make a stop useful. Avoid sizing every bay for an empty-to-full charge when your customers usually need a top-up. Record the answers by visit type rather than assuming every driver behaves alike.

Why does charging slow as the battery fills?

A charging curve describes how accepted power changes during a session. Energy Saving Trust notes that rapid charging slows at higher states of charge, including above 80%. That makes the final portion of a rapid session a poor basis for extrapolating the whole visit. It does not establish a universal cutoff for every vehicle. [S2]

For your site, this raises a parking question. A driver may remain in the bay while receiving less energy per minute. Decide how parking permission, charging permission and any overstay charge interact. Explain those terms before a session starts, and leave drivers able to follow their vehicle’s instructions.

Do not assume a driver who wants a fuller battery is using your site incorrectly. A rural onward journey or a fleet duty may need that energy. Plan bay turnover around actual customers and offer clear information about charging time.

How can you calculate a useful charging-time range?

Use energy divided by assumed average delivered power. The examples below use the 36 kWh battery top-up above. They exclude losses, interruptions and any time spent parking or starting payment.

These are arithmetic scenarios, not predictions for a particular car. A unit’s advertised maximum cannot be substituted for average power without checking the vehicle and session conditions. For procurement, request a range with those conditions written beside it. [S1]

Use the table to test your visitor pattern. Overnight guests can have a different charging requirement from drivers stopping briefly for refreshments. Compare AC and DC charging and dwell time before choosing the equipment.

What should you compare before ordering chargers?

Make a short schedule of vehicle groups, required top-ups and departure times. For each group, ask the designer to explain the binding limit: the car, charger or site supply. Ask how simultaneous sessions change delivery. This gives you something testable at commissioning rather than a general claim about speed.

Include these questions in your request:

• What energy can each vehicle group receive during its normal stay?
• Which assumptions change when the bay next door is occupied?
• What happens when a session starts at a higher battery percentage?
• How will staff distinguish a vehicle limit from a charger fault?
• Which session records can you export to review the original assumptions?

Network Rail discusses matching infrastructure to vehicle and site requirements. Use its framework to request evidence for the proposed design, rather than treating this illustrative arithmetic as an engineering specification. [S1]

After opening, compare actual session energy and duration with the procurement assumptions. Keep charging time separate from total bay occupancy: someone may remain parked after charging ends. That distinction helps you decide whether the next change should concern equipment, parking management or customer information.

What should you do next?

Prepare your visitor dwell times, fleet specifications if relevant and electricity information. Read what a site survey checks, then get matched with an installer that covers your area.

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