Two of the longest-range electric cars on the UK market, one road trip from Northampton to the Scottish Highlands, and a simple question: do these things actually go as far as the brochure says? Autotrader UK's Rory Reid and Alex Goy charged the BMW iX3 and the Mercedes CLA 250 Plus to 100 percent and set off north on a 500-mile run to Gleno. The BMW carries a 108 kWh battery and claims around 500 miles. The Mercedes uses a smaller 85 kWh pack but claims 484 miles by leaning on better aerodynamics and a lighter body. Neither car's trip computer believed the official numbers from the moment they pulled out of the services. The iX3's initial estimate settled around 420 miles. The CLA opened its range prediction at 410 miles. Real-world conditions tend to do that.
What makes this test worth attention beyond the entertainment value is what it reveals about two genuinely different engineering philosophies at the expensive end of the EV market. BMW's approach on the iX3 is straightforward: fit the largest possible battery and let capacity do the heavy lifting. The CLA's approach is the opposite, wrapping a smaller battery in a body optimized to waste as little energy as possible. In practice, through the first 225 miles the efficiency numbers were nearly identical: the Mercedes was returning 4.6 miles per kWh and the BMW 4.4. The gap was marginal. Pricing tells a different story. The CLA 250 Plus starts around 47,000 pounds in the UK. The iX3 sits closer to 60,000 pounds. That 13,000-pound spread is a meaningful part of the comparison that the range figures alone don't capture.
The cars reached their limits somewhere in southern Scotland rather than the Highlands. At 429 miles the iX3 pulled over at zero percent with a few miles of reserve likely remaining but no safe place to run them out. The CLA kept moving through the red zone warnings, finally coasting to a stop at 434 miles. A petrol Volvo XC90 running as the camera car was filled at the start of the journey and also reached its limit at 434 miles, with 50 miles of range still showing. That comparison is incidental to the main test but lands with some force: the gap between a modern petrol SUV and a top-spec electric saloon on a long motorway run is now measured in tens of miles rather than hundreds. The CLA's cabin was also significantly quieter than the iX3's, registering a 66.7 dB average against 84.5 dB in the BMW, and its infotainment proved considerably easier to navigate in timed side-by-side challenges during the journey.
Bottom line: Neither car reached Scotland on a single charge, but 429 to 434 real-world miles from electric cars that cost less than a base-spec Porsche Taycan is a different world from where this segment sat two years ago. The Mercedes makes the stronger case on value and efficiency. The BMW's bigger battery buys a small amount of extra peace of mind for roughly 13,000 pounds more. For most buyers doing the maths, that's hard to justify when the CLA is already this capable.