Comparison: BMW 60Ah i3 REx vs 2017 (94Ah) i3 REx

Test Drives | September 15th, 2016 by 20
BMW i3 red black 750x500

What a difference three years makes. I was able to secure one of the first 2017 BMW i3 REx cars that made its way into …

What a difference three years makes. I was able to secure one of the first 2017 BMW i3 REx cars that made its way into U.S. dealer inventory, compliments of Chris Chang, Sales Manager at BMW of Bloomfield here in New Jersey. The vehicle is mostly the same as my 2014 i3 REx, the one big exception is it has the new 94 Ah battery cells, which increase the overall battery capacity from 21.6 kWh to 33 kWh without increasing its physical size. That was necessary, since this isn’t a redesigned i3, so the battery modules had to fit in the existing battery tray.

bmw i3 60ah 94ah 750x422

The 2017 i3 REx in Fluid Black next to my “Moloughney Red” wrapped 2014 i3 REx

As much as I wanted to check out the moonroof option that this car had (finally the moonroof is available in the US!), there is no denying the single most important improvement I was interested in was to find out how much more range the new model has. The EPA range rating for the 2017 i3 REx is 97 miles per charge, and BMW claims 180 miles of total range when combined with the added miles from the range extender. The full 2.4 gallons of gas is now available for the REx. Previously it was software limited to only 1.9 gallons so the vehicle would qualify as a BEVx vehicle. My 2014 i3 REx has an EPA rating of 72 miles per charge, and BMW claimed a total range of 150 miles including the range extender miles. So the new i3 REx should offer about 35% more all-electric range, if the EPA test results are accurate. One thing to note is the auto manufacturers do the range testing in house, and reports it to the EPA. I think many people are under the assumption that the EPA tests the cars, and they do not. Manufacturers have been known to “massage” these numbers to fit their needs.

Range Testing

I wanted to perform three tests. The first was to fully charge the car and drive it easy. I didn’t hypermile, but I took it a little easier than I usually drive. It was 83 degrees, which is favorable for good range, but I did have the A/C on the entire time. I dove in Comfort Mode because that’s pretty much the only mode I ever drive in. I took a combination of highway and secondary roads and basically drove the speed limit with moderate acceleration from stops.

BMW i3 rex screen 750x422

After 100 miles of driving, the car still had 26% state of charge and was estimating an additional 37 miles available. I’ve driven my i3 long enough to know how far it can go, within a couple miles, and I’m sure if I were driving my i3 in those same conditions it would have gone about 72 to 76 miles before the range extender would have needed to turn on. This new i3 REx easily beat the 35% range increase expected by the EPA range rating. In fact, based on these results I think it would be hard for me to get less than 100 miles per charge even if I tried. So that’s what I did for the next test.

This time I was going to drive it harder. Not Autocross hard mind you, but I’d punch it from all the stops, drive 75 – 80 mph on the highway and not concern myself with using the regenerative braking to their fullest advantage. Basically, I’d drive like I was late to an important meeting. Halfway through, I realized my efforts weren’t making much of a difference. At 50% SOC I had driven 62 miles and the range estimator still showed 62 miles to go. I did noticed that the gas range estimate had dropped from 85 miles to 75 miles though, even without using any. That’s because my driving efficiency was much worse than it had been on the first 100 mile drive.


Seeing how I was still on my way to 120+ miles of range, I stepped up my assault on the tires, and really thrashed the car around a bit. It worked, and I further reduced my efficiency. I finished up this 100 mile trip with only 13.5% SOC and estimated 16 miles remaining. I was able to reduce the single charge range by 21 miles, but I couldn’t manage to get less than 100 miles of range, which was my goal. In my opinion this is great news. Honestly, I don’t know how this car is rated at 97 miles per charge; that’s nearly impossible to attain unless it’s being operated in cold weather or perhaps being driven at a very high rate of speed. I’m sure once the winter months roll in and the temperature drops it won’t be hard to get less than 100 miles of electric range. However in moderate temperatures, I think most people will always be in triple digits. Based on the experience with my car, I’m guessing this new i3 REx will probably average about 85 to 90 miles of all electric range in the winter. My car only averages about 60 to 65 miles of electric range when the temperatures are below 30 degrees Farenheight, therefore 85 to 90 miles sounds about right for this new, longer range model.

Even with trying to get less than 100 miles, I still managed 100 plus an estimated 16 miles remaining.

Even with trying to get less than 100 miles, I still managed 100 plus an estimated 16 miles remaining.

The REx Test

The final test was to see if the range extender performance was any different. Much has been made over the fact that the i3 REx can enter Reduced Power mode, and slow down under certain strenuous driving conditions. So I depleted the battery, drove it for 50 miles and made sure to take it up some hill climbs at highway speeds. The first thing I noticed is the range extender operates the exact same way as it always has. It doesn’t turn on until the battery state of charge reaches 6.5%. The “Hold State of Charge” option is still disabled here in the US, so if you want that feature, it will still have to be unlocked by coding the vehicle, as before. There was some speculation that the automatic turn on point of the REx might be at a higher SOC with the new model, but I can confirm that’s not the case. However, there were two observations that I noticed that were positive.

First, the range extender seemed quieter from inside the cabin. In my car, the REx motor is pretty quiet and unnoticeable until it kicks into it’s highest output mode. At that point you can definitely hear the scooter engine revving up high from underneath the rear seats. It’s kinda like your being chased by lawnmower. On long highway trips it will operate at its highest level for most of the journey and the noise is noticeable. I’ll usually turn the radio up a notch to cancel it out. With this new car, driving at a constant 75 mph to 80 mph the motor seemed much quieter than it does on mine. My wife was with me for part of this test and she also noticed. She actually asked me if the REx was even running. It seems to me that BMW improved the REx soundproofing. It does sound just as loud as before from outside the vehicle, but it’s definitely quieter on the inside.


Secondly, (and I’ve reached out to BMW for confirmation on this but haven’t received a response yet) it does seem like the REx motor has been tuned for a slightly higher output. I took the vehicle on highway roads that I drive on regularly, and have on occasion done so when the REx was operating. The range extender was able to hold the state of charge higher, and under more strenuous driving conditions than my 2014 REx can. There’s one particular long incline that I drive every day. With my car, if I start at the bottom with 6% SOC and drive 70 mph up to the top I’ll deplete the battery to about 2.5%. I did this same test with the 2017 car and I reached the top of the climb with 5% SOC remaining. I repeated the climb with the same results. I also noticed that I could drive at about 75 mph on flat ground and maintain the 6% SOC. My car can maintain the SOC on flat ground with a constant 70 – 72 mph, but not any higher or the charge will slowly deplete.

I know the 6.5% buffer is now larger, because it’s holding 6.5% of 30 kWh instead of 6.5% of about 19 kWh, so that extra energy is definitely helping, but to me it appears that the REx motor has a higher output for the 2017 model. The REx motor in my car is rated at maximum power output of 28 kW. I wouldn’t be surprised it we find out the power has been increased to about 33 kW, but I don’t have any official confirmation on that. I’m just going on what I’ve experienced with the previous REx cars and how this new one compared to it. Another hint that I may be correct is the REx is now rated at 35 mpg, down from the 39 mpg which the previous models were rated at. I don’t think the extra 170 lbs alone would cause a loss of 4 mpg. I believe it working harder now to produce more energy, which was I’m guessing was achieved through a software adjustment.

After driving 42 miles on the highway I still had 70.5% SOC and an estimates 93 miles or range remaining. My 2014 i3 REx doesn't even go 93 miles per charge! The range of the 2017 is a substantially greater than previous i3s, even more than the EPA rating would seem to advertise.

After driving 42 miles on the highway I still had 70.5% SOC and an estimates 93 miles or range remaining. My 2014 i3 REx doesn’t even go 93 miles per charge! The range of the 2017 is a substantially greater than previous i3s, even more than the EPA rating would seem to advertise.

Faster Charging With A New Profile

Previous model year i3s were capable of charging at 30amps which, at 240 volts, gave a maximum draw of 7.2 kW. The new i3s can accept 32 amps which translates to 7.4 kW. Not a huge difference, but it can help if you’re waiting for the car to charge to a certain SOC so you can unplug and drive. I should note that most public charging stations are limited to 30 amps, so it won’t make a difference on those units. However at home, I have charging stations that can deliver 32 amps so I was able to monitor the difference. My car usually accepts 7.1 to 7.2 kW (depending on the voltage supply) but this new i3 was consistently drawing 7.3 kW to 7.4 kW, so I can confirm the onboard charger upgrade.

bmw-i3-charge-rate bmw-i3-charging-details


The charging profile of my 2014 i3 REx is on the left, and the 2017 i3 Rex is on the right. 
Both charged from 6.5% to 100%. The 2014 car charges fully in about 3.5 hours and the 2017 in about 4.5 hours.

I did observe something interesting while monitoring the charging profile of the new i3. Instead of the charge rate gradually tapering off as the SOC reached 90%, and slowing down for the final 40 minutes of charging, this car took the maximum rate nearly right up to the end of the session. I charged it three times to monitor this and it behaved the same way all three times. I’ve never observed this on any other EV. Normally, the vehicle slows down the charging rate considerably as it approaches the end of the session to slowly balance the cells. This takes place once the vehicle is over 90% and the final 5% to 10% of charging takes much longer than charging at lower SOC. That’s not happening with this vehicle. It only slows down slightly, and only for a couple minutes at the very end. The charging rate doesn’t gradually lower until it shuts off, it more closely resembles falling off a cliff. Interesting.

Finally, a Moonroof


The moonroof is a new option for the US. It’s been available all along for i3s outside of North America, and now it’s available here also. The moonroof is a $1,000 option and is a split version, having two openings separated by a solid center section. Each opening has its own manually-operated sunscreen, but the moonroof itself is one piece, and slides back with a push of a button. However it only opens about eight inches, slightly more than half of the actual opening in the roof. It’s not even large enough to stick your head out of it – not that you would want to do that; but the point is, it’s a small opening. The moonroof does accomplish two things, though. It allows more light in the cabin, giving the feeling of it being more open. It also allows you to eliminate side window buffeting by simply tilting the moonroof open.

Available Battery Capacity – Surprise!

BMW states that the new battery is 33 kWh, and 27 kWh of that is usable. That’s only 81.8%  of the total pack, much less than the ~90% they allowed to be accesses on the 60 Ah battery pack. When I read that I wondered if it was perhaps sign that the new 94 Ah cells were less tolerant to deep discharge than the 60 Ah cells were, so BMW was going to be conservative with them. So when I fully charged the battery after the first 100 mile test run, I checked the hidden diagnostic menu and to my surprise it was showing a full 30 kWh accessible. So BMW is allowing access to roughly 90% of the overall pack, just like they do with the 60 Ah cells. That explains the extra range I’ve witnessed but it doesn’t explain why BMW’s official stance is that there is only 27 kWh accessible. Perhaps it’s for battery capacity warranty claims?

While the "Batt.Kapa.Max" isn't an exact measurement of the available capacity, but it is very close. Close enough to prove there's much more than the 27 kWh that BMW claims is available.

While the “Batt.Kapa.Max” isn’t an exact measurement of the available capacity, but it is very close. Close enough to prove there’s much more than the 27 kWh that BMW claims is available.

Gained Some Pounds

The only negative I’ve found is that the new battery is heavier, and adds 170 lbs to the curb weight (3,064 lbs to 3,234 lbs). This does effect performance a bit. The car doesn’t feel quite as responsive as my 2014 does. Without testing the performance times, I’d say it’s probably close to a half a second slower from 0 to 60 mph. Handling didn’t seem quite as crisp as mine either, but that might not be this car’s fault. It has the 19″ turbine wheels, and my i3 the 20″ wheels with the sport tires, which are wider and have a larger contact patch. I also recently lowered my car with sport springs from H&R which have improved the handling, so it’s not fair to compare the handling to my car.

 My i3 before and after installing the H&R Sport springs. It dropped the car 1" in the front and .8" in the rear.

My i3 before and after installing the H&R Sport springs. It dropped the car 1″ in the front and .8″ in the rear.

The other performance change I noticed is the regenerative braking seems to be blended in differently. When driving slowly, it seems pretty much the same as my car does. However at higher speeds the car will coast more when releasing the accelerator. The regenerative braking doesn’t initially come on as aggressively as is does on my car. It will get progressively stronger if you continue to coast, but initially upon releasing the accelerator, the car freewheels a lot more than previous versions do. I like this for highway driving, as freewheel coasting improves efficiency. If you slightly depress the friction brake pedal, the friction brakes aren’t used, instead the car used first uses only regenerative braking, until you depress the brake pedal harder.

Summing Up

After a couple days and driving over 300 miles I feel it’s safe to say that I believe most people will find the average usable range greater than the EPA rating of 97 miles per charge. I almost wonder if BMW purposely underestimated the range a bit in an effort to under-promise and over-deliver. On my 2014 i3 REx, I’ve found the range to be pretty close to the EPA rated range. of 72 miles per charge. I do average a few miles more than that during the warmer months, and about 10 miles less per charge during the winter when it’s cold. But this new i3 has unexpectedly trounced the EPA range rating by a healthy margin. I think most people should average well over 100 miles of pure electric range on these vehicles. The range increase will undoubtedly push some people deciding on whether to go BEV or REx into the BEV camp. I know if I were buying one today I’d go BEV also. Getting this kind of range with the REx, I’m certain 125 to 140 miles per charge would be easy to attain with the 2017 BEV. That, combined with the ever increasing CCS DC fast charge networks, would really be all I need for all my driving needs.

bmw-i3-comparison bmw-i3-red-black

Thanks again to Chris Chang and BMW of Bloomfield for providing me with the use of this car for three days of testing.

20 responses to “Comparison: BMW 60Ah i3 REx vs 2017 (94Ah) i3 REx”

  1. Tom Hilton says:

    The choice of going REX is surely very little to do with range, but everything to do with refuelling on the road.

    • Tommolog says:

      Certainly for some, Tom but that’s not always the case. It depends on what the vehicle is used for. Even so, with the rapid deployment of DC Fast charge stations in some areas, that’s becoming a non-issue for many people.

      • Tom Hilton says:

        A DC fast charger that can deliver 80 miles in 2 minutes won’t happen though will it?

        • Viking79 says:

          It is possible, but you are talking 1+ MW power. Probably need some sort of capacitor (flux? :) ) at the charge station to shield the grid from the spikes.

          • Tom Hilton says:

            Quite so. I think the laws of physics make REX sensible while battery energy is still so expensive. And that is all about refuelling rates, rather than range. Even Tesla refuelling rates, whilst stunningly good, are lower than ICE by a factor of 10.

        • Tommolog says:

          BMW and partners are working on DC fast chargers that will deliver 300 kW which would translate to 40 miles in 2 minutes, and possibly more if the vehicle is more efficient than their current offering, the i3 is.

          But to me, that argument isn’t a relevant one. I understand why people that haven’t owned an EV would focus on recharge times, but it really depends on your driving patterns and needs.

          I’ve owned EVs for the past 6 years and have driven them 200,000 miles. As much as you would think charging might be a hassle, it isn’t. It seems that some people focus on these long trips you need to make. How often are they necessary. Maybe two or three times a year I need to drive more than 150 miles to a destination. Sure there are real rural parts of the US that require people to drive long distances for everything, and for those people I’d agree a plug in car probably isn’t the best choice. But I leave my home charged to 100% every day and have about 90 miles of electric range followed by an additional 60 miles of range on the REx. It’s just not necessary to worry how long it takes to charge, I’m sleeping when my car charges every night.

          Then on the road when I do make those occasional long trips I stop after two hours of driving for 45 minutes and I’m good for another 2 hours of driving if needed. I prefer to stop after two hours anyway, to stretch my legs, use the restroom and gram a bite to eat or a coffee.

    • Sander says:

      Just last friday evening I arrived at my destination with 14km range left. The chargepoints all gave an error when I swiped my card. After several long phonecalls my card turned out to be terminated last july (don’t know why yet, will have to call back tomorrow).
      Luckily I could fall back on the rex. With only 6km of fuel left I had to fill up within 20km. Last time at the gas station was months and more than 6000km ago! So for me, rex is also about insurance.

      In the mean time I’ve ordered a second card from a different provider for back-up.

  2. Sander says:

    Very nice article, thanks!
    I would like to note that the moon(?)roof lowers the ceiling for the passengers.
    And of course you can also coast with the pedal if you keep the powerdial exactly in the middle.

  3. Howard says:

    Nice comparison. I am bit of an i3 Newbie … own a 2014 BEV that I bought lightly used. Perhaps not the right place to ask but what app/system did you use to generate the charging detail/profile picture?

  4. Viking79 says:

    Manufacturers don’t massage the EPA tests unless they want to be sued later (it has happened, Ford, Hyundai, and others have been forced to lower claims on cars before). The EPA is open to do the tests as well, so it doesn’t pay to cheat on those.

    However, companies do tricks to maximize EPA numbers of course, turbos for example on ICE. Tune it so it does well on test, but maybe not as well in real world unless you drive like the test.

    • Tommolog says:

      In this case the numbers are overly conservative, so there would be no basis for a lawsuit. It would be like suing over getting 30 mpg when the car is advertised as offering 25 mpg! ;)

  5. lgg4 says:

    Tom, great write up! Will be interesting to see how the BEV does in the real world. Any way you can get a ahold of one of those and do a similar test?

  6. Devin Serpa says:

    Thank you for the detailed report.

    Glad to see the new i3’s range isn’t as squishy as the 2014, on the BEV this was detrimental.

  7. Fusiongt says:

    I wonder if the regen breaking changed at all or if it’s simply the car weighs more now and so when you’re going 70+ mph and let off, it’ll take longer to coast with the added ~160 extra pounds. I imagine they haven’t really tweaked the i3 more than the battery and so all the extra weight is making it a bit slower and also “coasting” more. Probably not very noticeable but I’m pretty sure it’s not something BMW intentionally did.

  8. madskills says:

    WOW! Thank you so much for your comprehensive, capability review of both the 2014/2017. I would love to buy a 2014 Rex if BMW would do the software upgrades, from tuning the Rex, increasing the fuel tank level and possibly allowing the Rex to handle a proper speed on the interstate. I live in Florida and it would work as a second vehicle(especially for the beach).

  9. […] of April. In Norway, the tenth-thousandth BMW i3 was already handed over to customers, since the introduction of the new 94Ah battery, the electric car has enjoyed great demand all over the world. With the facelift scheduled for this […]

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