Is REx worth it?

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May 6, 2022
Hi There,

I'm in the process of looking for an i3 for my wife as her commuter vehicle and I have a couple of questions.

We recently moved to the Birmingham area of the UK from Canada and she has a commute of about 20 miles each way. Her work has several level 2 chargers set up (I think they are 6kW) so there should be no problem for her to get an opportunity charge while she's there. We can also install an L2 charge point at our home if needed.

I currently drive a 2017 Lexus CT200h, and she is replacing a 30kWh LEAF that had a pretty degraded pack (I was estimating about 21-22 kWh) based on charge times and the GOM.

For longer trips, my hybrid would be the one we would take.

We are looking at 2018 and up i3s for the larger pack and I am debating looking for one with the REx. We'd both rather be full EV, but range anxiety is real, (especially after owning a LEAF).

1) Is the REx worth it in this situation and, 2) are there any known reliability issues with the Rex that I can be aware of in order to avoid?

I remember in UK there were road tax implications for REX. Not sure if it will impact your situation.

The 94ah can do 100-130 miles. Based on your description I think a BEV could be a better choice. Why not spend the REX money on a 120ah BEV model?
I think the road taxes are in urban areas like London (ultra low emission zones). Not really too much of a concern because we are a couple of hours drive from there.

I wasn’t aware of a larger battery than the 33 kWh pack, so I guess I need to do more research. A 40 would totally meet the mission with room to spare, as would a strong 30. We are just a little gun shy from the LEAF.

Thanks for the input. I’d much rather not have an ICE at all these days.
The 2017+ 94 Ah packs appear to be far and away superior to the notorious Leaf batteries. I could reliably get 130 miles out of mine on a full charge, although I normally kept it below 80%. I was regularly driving a daily 40+ mile commute in that car and mainly L1 charged it at work for 8 hours at a time. The DCFC coverage in my region is sufficient that I never hesitated with longer drives (not really road trips) without doing much in the way of planning. On the occasions I did need to charge while out, I could generally count on a 30 minute no-fuss stop to get me back to 80%.

I went into i3 ownership with a predilection for BEV. I just wanted to be done with ICE. I understand some owners / prospective owners have a genuine need for the REX, but it seems to me many want it as a security blanket, and many report back here and on the other forums / Facebook that they rarely use theirs. And of course there are those who run into maintenance problems who regret having it.
Thanks, the first hand experience is really helpful. There are many DCFC here as well and we too just want to be done with ICE.
The BEV i3 used market seems a lot more robust here anyway.

Having REX definitely has its advantages, but if you have a hybrid car those are less important. If I had a hybrid as a second car, I would have bought a 130ah BEV.
Is there an easy way to differentiate between the 130Ah versions and the smaller battery pack?
I find it kind of odd that BMW used Ah as the capacity metric. kWh is a far more universal measurement.
By the way, what is the pack voltage? Haha
Sorry, I meant 120ah. There is no visual difference. I am not sure about UK, in the US 2018 model years are 94ah and 2019s are 120 ah. I am pretty sure in UK 2019 are 120ah, but I am not sure about the cutoff date in 2018 models. One way is to check the VIN using a BMW VIN decoder.
I replaced a 60AH REX with a 90AH BEV and never looked back. i3 isn't a good hybrid. The engine is annoyingly loud and buzzy, the fuel economy isn't great. If you look around this forum, you'll see that engine is one of the most problem prone components.
That’s exactly what I have been thinking. It seems like either get a BEV or not (or get a full hybrid or not). Toyota seems to have perfected the hybrid, but I am so over oil changes and assorted ICE maintenance.
i3 is a "series hybrid" where the engine never drives the wheels directly, it is used only as a generator. This architecture introduces additional drivetrain losses.
Here is the engine technical training material, if anyone is interested:

This is for the 60ah models, the newer models have slightly more power (38 hp instead of 34), but basically the same engine. It is a simple engine, port injection, mechanical oil and water pump. It has forged crankshaft and connecting rods. Run it once or twice a month for 10 minutes, it will be reliable.
Pretty sure you’ll be taxed on this vehicle with REx. Check out Government site to check prior to purchase. 2015 REx for example will be zero road tax.

Back to your dilemma. Charging infrastructure is changing all the time. The larger battery helps of course, but back up REx is attractive. The i3 is fun to drive, but the suspension is unforgiving. Watch ones with 20” wheels. Standard 19” wheels are fine.

If possible get all the toys. Harmon Karon sound system and leather interior. Some of the cloth interiors look great but are impractical in the UK in our inclement weather.

Back to REx. It needs annual service, so oil change, etc. Run it regardless, at least a couple of times a month. Warning messages such as engine management light can be expensive. Known faults are tank pressure sender, hopefully resolved on newer models and fuel pump relay that lives under passenger dash is inexpensive fix. There’s also a NOx sensor if it all goes south. Uses a good Indy not main BMW dealer unless you want to spend cash and replace parts until they find the problem. If your spanner handy, then BMW ISTA software is sound investment, clearing parking sensor faults to airbag light resets.
Back in time, Rex could be a good alternative to have longer mileage & safety for some areas with less charge stations. From now on, in my opinion 120ah should be the way to go. The mileage has doubled since the 1st version of i3, the charge stations are quite increased in number. No need to carry an ICE with you all the time & deal with its annual service anymore.
No need to carry an ICE with you all the time & deal with its annual service anymore.

I just had my service done (2018 i3 rex) and it was relatively simple - an oil change and a brake fluid change. I was going to do it myself (and even bought a T20 driver) but the labor was pretty reasonable and as an amateur mechanic I didn't want to mess with my brakes. A BEV model would still need the brake fluid change.

This is my first EV, and the REX is a nice "bridge". I figure my next car will be an EV with over 200 mile range and I won't have a need for a range extender. My car only has 17k miles on it, I've got some time to enjoy my i3 until then!

In reality, I'm in a 2 car family and work from home. I never need the REX in normal driving, but it's nice to know it's there when I take longer trips, to figure out where the chargers are.

I work at a company that makes intelligent hybrid solar/battery storage systems for businesses and municipalities. We had 4 level 2 chargers using our systems and offered free charging. I miss working at that office now... :)
Back in time, Rex could be a good alternative to have longer mileage & safety for some areas with less charge stations. From now on, in my opinion 120ah should be the way to go. The mileage has doubled since the 1st version of i3, the charge stations are quite increased in number. No need to carry an ICE with you all the time & deal with its annual service anymore.
There are still highly regional dependent discrepancies with that line of thinking - and consequently places near me even a 120Ah pack cannot reliably take me to. US charging networks still completely suck, even where chargers are SUPPOSED to be working. The REx has made that a non-issue for me on multiple occassions.
My experience with a 2016 REx in Florida mirrors ksnax’s above. I use the car right to the limit of its battery range for my commute and the range extender makes it doable during cold weather, heavy rain or headwinds. Code the car for “hold state of charge” like others have advised & the REx really shines.
I’ve had no mechanical faults; change the oil & filter like any other piston engine & motor past the broken charging network.
For my use case, range extender makes the car viable.
I agree with briantompo. 2014 Rex 42000 miles. Tiny battery but still no worries if suddenly I need to go twice as far as planned. Good deal for me.
I have a 60ah rex and love mine, ive had a problem with the rex but that was software related not engine. I very rarely use public chargers, just charge at home or work and if i need to do a long unexpected journey i use the rex