Battlow pyramid

BMW i3: Range Extender

As range provided by electric cars is not that big, and there are not so many charging points, Range Extender is still a must for me. Even if there were more of them, in some circumstances it takes too long to recharge a car such ofen when you are facing a long journey.

Range Extender works pretty well in the BMW i3, but it must be improved to give the user more control and to be much more effective.

Maybe the car was conceived for short distances, and it’s not made for long trips. My guess is it was conceived as a car-car, but batteries forced BMW to be cautious in the message to avoid harming the new line because of a wrong promise.

But BMW i3 Range Extender is a real car. It’s a 170 horsepower BMW car with a battery and a fuel tank. It MUST be able to perform a long trip even when it’s necessary to refuel several times.

Facing a long trip (>300 Kms), this is theĀ  “Battlow Pyramid” for me:


  1. First of all, obvious: it’s absolutely mandatory to arrive.
  2. User must not fear at all that not arriving is even a possiblity.
  3. User must be able to drive at a normal speed
  4. Trip should be as comfortable as possible. No fridge/oven feeling.
  5. It’d be nice if it’s also economic
  6. Ecology makes the top of the pyramid.

How it works, and how it should work:

First of all, “Range Extender” is a fuel powered engine that produces elecricity that can be used by the electric engine of the car. The fuel engine is much less powerful than the electric one, so in certain circumstances, battery keeps draining even with the Range Extender powered on.

It’s supposed that the Range Extender power goes directly to the electric engine, but it seems logical that the path goes through the batteries, so the energy could be stored. This would explain why in some cases, fuel engine is running with the car stopped (otherwise this energy would be lost, and it’s not).

When the user enables the Range Extender, a white arrow appears in the charge indicator. This will be the target charge for the car from this moment. The fuel engine will power on and off, slower and faster, accordingly with car speed, so that the charge level can be kept at this level of charge.

There are several problems in this behavior:

  1. Range Extender often fails to keep the charge level in fast roads.
  2. Target arrow is lost when car runs out of fuel or stops.
  3. The car doesn’t know what the user wants to do along the day, but acts as if it knew.

So, for example, a user plans to move to another city at, let’s say, 300 Km, using a highway with 120 Km/h speed limit, to keep on driving in this city along the day, and be back to home at night. User may not have chance/time to use any charging point.

Trip starts wit full fuel and battery. When charge drops below 75%, user has to remind to start the Range Extender.

If it worked as expected, It would be possible to arrive to the target city with 75% battery, drive in pure electric mode along the day, and be safe back at home, keeping last 30% battery at the end of the journey, once close enough.

But… while possible, it’s tough to achieve, and forces the user to take care of many parameters that should be managed better, and automatically.

First of all, it’s not possible to enable Range Extender until battery is below 75%. It would be a good first improvement just to allow the user to enable it at the beginning, even if the charge is 100%, just to avoid the user to take care of it while driving. The arrow could be set anyway at 75% if enabled when charge is above.

Second, the arrow must be kept where placed, no matter if the Range Extender runs out of fuel or user parks the car. These events don’t mean at all that that the necessity to save battery has dissappeared.

Continuing with the journey, imagine the user takes care and sets the arrow at the very first moment it’s possible. The car run in Range Extender mode, and battery tries to keep (more less than more) in the target charge level.

But at some moment, the Range Extender runs out of fuel. Each meter the car advances in pure-electric mode, drained battery will never be recovered, because the arrow dissapears.

Once refuelled and started again, the car not only has forgotten where the arrow was, it has also forgotten there was an arrow, so the user is again obblied to take care to manually start the Range Extender, and it will start with a new arrow in the current battery level that, again, the Range Extender will fail to keep in fast roads.

The option is to refuel before running out of fuel, but mind the additional stops because of underusing a small deposit, and even so, mind also that the gap between original target and real battery level at stop, will be lost once refuelled.

With all this, at the end of the journey, the user will probably run in noisy fuel mode inside the target city, will be back home with no AC/heating and, if lucky, only fearing not to arrive home at a normal speed.

“Make things as simple as possible, but not simpler”.

The problem I see here is that BMW tried to keep them ‘simpler’.

User experience could be really reinforced just with adding some control of the arrow (up/down) without complicating the interface, adding an “aggressive mode” for emergencies, and making some minor improvements.

This is how I’d expect it to work:

  • It should be possible to enable “Range Extender” always
    • Even when there is not fuel to run (alert, but enable and place the arrow at current charge level)
    • Even when charge level is above 75% (place the arrow at 75%).
  • Arrow should be kept until user disables “Range Extender” or car is plugged.
    • Even when car runs out of fuel (alert, but keep the arrow where it was set)
    • Even when the car is parked (keep the arrow where it was, when restarted).
  • It should be possible to move the arrow up and down to give the user the opportunity to decide the target charge in coherence with the planned journey.
    • “Target level” line in the menu, manageable through the command wheel could be a proper place. If previous stories have been done, user could set-up this charge level at the beginning of the journey, before start driving, and keep it until safely close to home.
  • “Agressive mode” Range Extender should be available for special circumstances where the user needs to get the maximum possible power from fuel in the minimum time, no matter if the car is in movement, or how fast is it going.

If these ‘stories’ above were executed, I’d consider the BMW i3 a perfect vehicle to use in the city, and also to do sporadic long trips without worrying about range or being forced to find and stop (if available) for a while in a power charger.

Maybe this way it would not be the most comfortable vehicle for long trips, because of the amount of (at least safe and fast) stops, but perfectly able to do them.

At the moment, it’s ‘able’, but not comfortable at all due to range anxiety and frustration it can provoke if not handled very carefully.


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