Did you know that when you use a rapid public charger, you pay for the total energy consumed by the charger in AC and not for the energy that arrived in your car in DC? AC to DC conversion leads to losses in the form of heat; when expressed as a percentage of net charge vs billed charge, we get the charging efficiency of the charger hardware.

Why is this important?

When you fill-up an ICE car with petrol or diesel, we pay for the exact quantity of fuel delivered to the vehicle in litres. If the forecourt has a leaky point that wastes fuel, we can report and easily get the money back. Forecourts are even mandated to test their pumps for accuracy periodically.

There are currently no regulations or testing regarding the losses for public EV charging. Let us assume the following:

A charger that charges 49p per kWh has a loss of 10%. When you top up for 40kWh, you pay £19.6. However, after the losses, your car might have only received 36kWh, which must have cost you only £17.6. £2 overpayment would be for the charging losses with the hardware, which unfortunately is passed on to the customer. The only exception appears to be the Tesla Supercharging network which only charges for the energy that arrived in the car, excluding the losses. Tesla is also generally cheaper at around 42p for 150kW. Therefore, it represents great value for money but is only available for Tesla owners.

For this blog, we visited two Allego (Shell Recharge) and three Osprey chargers over different days to measure the charging efficiency. We used the same Tesla Model Y car during the tests. And we took care to avoid coldgating and prevent heating or music from getting used during the charging session. The results are below.

Charging Efficiency comparison for Allego and Osprey Charging


Allego (Shell Recharge) had the lowest charging efficiency at around 90% compared to Osprey Charging. The low efficiency is not a one-off observation since I have used one of the Allego chargers near my house for over a year and observed this large discrepancy over time.

The charger hardware used by Allego is an Efacec QC45.

Efacec QC45 Technical Information

With a power factor of 0.98 and a rated efficiency of 93%, the real world efficiency of around 90% is adequate but not great. Also of interest is the nominal power of just 45 kW continuous. During my charging sessions, I noticed the power fluctuating between 46 kW and 47 kW, which is acceptable but not market-leading.

One of the Allego chargers I visited operates with a lower power output of 22 kW. Even the lower power output did not improve the charging efficiency beyond 90% for Allego, indicating the limitations of the hardware.

22 kW (instead of 50 kW) charger at Hunton Bridge

Osprey Charging

I visited a 50 kW charger (Tritium RT50) and a 75 kW charger (Tritium RTM 75)

Osprey Tritium RT50

Osprey Charging at Bessemer Road uses Tritium RT50 with a rated efficiency of 94% and a power factor of 0.99 yielding a real-world efficiency of over 93.5%

Osprey Tritium RTM 75

The charger at London Road uses the improved Tritium RTM 75 model with slightly higher efficiency of 95% and a close power factor of close to 1.

This charger gave the best value for money with a real-world efficiency of over 94%.

The Tritium chargers also consistently delivered 48 kW power to the car, which is 1kW more than Efacec had managed.

Closing Thoughts

With a cheaper rate, quality hardware, and better charging efficiency, Osprey was around £3 cheaper on every top-up than Allego. While this blog covered a single aspect of efficiency, other factors related to the battery and the motor in an EV could determine the overall tank-to-wheel efficiency.

EV Overall Efficiency

The overall efficiency of an EV is significantly higher than an ICE vehicle, as shown. Consequently, the individual charging efficiency of rapid chargers should not deter any prospective buyer from owning an EV since the benefits far outweigh these costs.