Buying a Private Party 2015 i3 Rex with 68K miles. Good Idea?

I am planning on buying a fully loaded with all options i3 Rex with 68K miles. The car has been maintained well and has 3 more months of CPO left.
Should I be staying away from a car this high in miles? I used to own a 15 Rex but sold it last year and have been missing the car ever since. Should I be worried about buying anything without any warranty?

The answer depends on whether you can afford to eat the cost of a major repair. The i3 seems to be a pretty reliable car, at least compared to other BMW models, but every car will eventually break. BMWs, for whatever reason, cost a fortune to fix when they break, so this can be a really bad life event.

Let's take a concrete example. Let's say that, a year from now, the REx stops working (I'm NOT saying that this is likely. I have no idea how reliable the REx is, but it's possible). You will need to take it to a BMW shop to diagnose the problem. Let's say it's something major and the engine needs to be rebuilt. Hardly anyone is going to want to touch an oddball little derated scooter engine they've never seen before, so that means you'll be replacing the whole REx. I'm going to guess that the cost of doing that will be close to $10,000 at a BMW dealership, but someone please correct me if I'm wrong. Probably somewhat less at an independent BMW garage, but just the engine assembly parts will be five grand, brand new. That's a huge amount of money for a car that is worth less than $18k right now, and still depreciating.

Anyway, the point I'm making is that when you buy any used car in as-is condition (no warranty) you are taking a risk. Just be sure that you understand the potential risk and are prepared in case something goes wrong. Being "prepared" may mean having money in the bank to pay someone to fix the car, or having money in the bank to replace the car, or having the time and know-how to fix the car yourself. Just have some kind of Plan B.

My Plan B was having a CPO warranty and paying for a warranty extension out to 2023, but your Plan B might be something different.

As a non-Rex owner, I haven't done a ton of research on it but from what I've seen around here it seems like some of the issues with the REX stem from not using the engine frequently enough, so ironically a car with lots of miles might be better in that regard if a decent amount of those miles were on REX power. I don't know if it's possible to check REX runtime.

The battery, on the other hand, will be worse off due to the # of cycles so you'll almost certainly notice degradation but how much will depend on a ton of factors. In theory, you'd still have ~38k miles or a few years left on the battery warranty.

So, I wouldn't rule it out entirely but as richs says, there are some additional risks. Purchase price and your expectations should be adjusted accordingly.

I've only owned my 2017 REx for three months so far, but I can say that the vast majority of the 4000 miles I've put on it are electric. I've filled the little gas tank a total of three times, I believe. Apparently, though, the car itself will fire up the REx periodically if you don't use it. Whether that automatic REx cycle is enough to prevent engine problems due to lack of use is open to debate, so I burn through a couple gallons of gas every month and get the engine fully warmed up just to be sure. I doubt most owners worry about this, though.

Anecdotally, the 2014-2016 battery (the 60 Ah) seems to have a lot more issues with degradation than the 94 Ah. Won't go into the reasons for that here since that's been hashed out before, but that's something to really think about with a 2015 i3 with 68K miles. The eight-year battery warranty only has a couple years left, and it sounds like getting that warranty honored by BMW in borderline cases is not easy. Checking the battery capacity ("Batt. Kapa. max") in the service menu, while not a perfect indicator, gives a rough idea of how degraded the battery is and should definitely be looked at before buying any used i3.

These are just things to consider, though. The selling price factors so much into the calculation of whether the risks are worth it. The lower the purchase price, the less money you are risking losing. And, of course, you should get any used car checked out by a mechanic (preferable one with some EV experience) before you buy it.

I think some of the problems with the REx come from moisture. Depending on where you live and whether you charge through puddles at speed could also make a difference. Running the engine generates some heat and that may help to dry things out, that assumes you can get it started!

I live in So Cal with a drive of 36 miles RT. The car I'm buying has been driven on Rex a lot as are others in Socal. I'm getting this for 11.5K.
Other than reading about issues with 2014 model Rex cars, I thought the later model Rex cars were solid? Is this not the case?

If the vehicle goes to the dealer at the recommended intervals, many little things get fixed along the way. Stuff that may have been true initially, may not apply anymore if that was done. In general, the i3 has been pretty reliable.