BMW i3 Range Extender Explained: Is REx Worth It in NZ?

The BMW i3 REx is one of the more unusual EVs on New Zealand roads — a battery-electric car with a small petrol generator on board purely to extend range, rather than to drive the wheels directly. It's a clever idea, and one that still divides opinion among owners. Here's how it actually works and whether it's worth seeking out.

How the range extender actually works

The REx system uses a 647 cc two-cylinder petrol engine, originally derived from a BMW motorcycle design, mounted alongside the electric motor at the rear of the car. Critically, this engine never drives the wheels — it exists purely to spin a small generator that tops up the battery once charge drops to a low reserve level, giving you extra range to reach a charger rather than genuine unlimited petrol-powered driving.

Most i3 REx models sold into NZ arrived as used imports from the UK or Japan, and typically carry a fuel tank of around 9 litres — enough for roughly 100–130 km of extended range once the battery is depleted, on top of the car's normal electric-only range.

Electric-only range by generation

• 60Ah pack (2014–2016): around 100–130 km real-world electric range
• 94Ah pack (2017–2018): around 150–180 km real-world electric range
• 120Ah pack (2019–2021, REx availability varied by market): around 200–230 km real-world electric range

Add the REx's roughly 100–130 km of petrol-generated backup range, and even an early 60Ah REx can realistically cover 200–250 km between a home charge and a petrol stop — genuinely useful for buyers nervous about range anxiety in a car this old.

Is REx worth paying extra for

Used i3 REx models typically command a $2,000–$4,000 premium over an equivalent battery-only i3 in NZ. Whether that's worth it depends entirely on your driving pattern:

• If you regularly drive beyond your electric-only range and don't have reliable fast-charging access along your route, REx genuinely solves a real problem
• If your driving is predominantly local with a home charger available every night, the battery-only i3 is simpler, lighter, and has one less system that can develop a fault

The maintenance trade-off

This is the part that catches new REx owners out. Because the petrol engine is used so rarely — often just to top up charge on the occasional longer trip — it still needs the same basic care as any small engine: annual oil changes, spark plug checks, and periodic running to keep the fuel system in good condition. Owners who never engage REx mode for months at a time risk fuel going stale and can develop starting issues when they finally do need it. We recommend running the REx generator deliberately at least once every few weeks, even if you don't need the range, purely to keep the system exercised.

Common REx-specific costs

• Annual REx engine service: roughly $220–$320
• Fuel system issues from prolonged disuse: $150–$450 depending on severity
• REx-specific fault codes relating to the generator control unit: typically $300–$600 to diagnose and resolve

Our take

The range extender is a genuinely clever engineering solution to legitimate range anxiety, and it works well for owners who use it as intended — as an occasional safety net, not a primary power source. But it does add a small petrol engine's worth of maintenance complexity to what's otherwise one of the simplest cars to own. If your driving pattern rarely needs the extra range, save the premium and buy a straightforward battery-only i3 instead.