Question on battery heath vs. range vs. kapa

[Chris94]

Hello,
New to posting here, but have found the forum to be very helpful as I look for a used i3.

I am looking at a 2017 Rex that was purported to have "very good" battery condition. When I went to test drive I was a bit alarmed to see the battery bar showing Full and a battery range of only 54 miles. I test drove a few miles and the range figure dropped accordingly. The car had been in a cold environment (10 degrees F, -12 degrees C) for a couple days. Following the drive the car was parked in a warmer (well above freezing) parking bay while I inspected the car. After a while I noticed the range increasing to 74 miles just sitting there with the car turned on most of the time. I had to leave, so I couldn't verify if the range would go even higher.

I found the kapa to be 28.1 kWh, which seems to be a pretty good value, but I have read here that kapa isn't everything when it comes to battery condition.

When it's cold, does the range improve after driving for a while as the battery gets to its ideal temperature? So, if I set the car to be ready at a certain hour, will it warm up the battery in advance? I don't want to have 50 miles of range, so I'm hoping I can get some insight from this group.

Other than this issue, and a damaged plastic jack point insert, the car drove well, despite having ecopia tires (I have already arranged for a set of blizzaks on spare rims if I buy the car.)

C94

 

[mojo]

When it's cold, does the range improve after driving for a while as the battery gets to its ideal temperature? So, if I set the car to be ready at a certain hour, will it warm up the battery in advance?

Provided you don't need to exploit any EV-specific electricity supply tariffs then yes. If you are able to plan for your charging to complete just before you are due to leave then the battery will already have been warmed a little by the charging process (the degree of heating depending on the rating of charger that you use). That effect can be augmented if you set the car to carry out "battery preconditioning", which is where it uses power from the EVSE (charge point) to warm up and maintain heat in the battery during the 3 hours before your departure time.

Also, as you've already noted, if you are able to store and charge the car inside a garage that will help too, slowing the rate at which the battery cools after charging, and reducing losses to the surroundings while preconditioning is under way.

Unfortunately many EV-specific electricity supply tariffs completely preclude battery preconditioning, because of the rather limited design of charge scheduling that BMW saddled the i3 with. It's a price that some of us have to pay for cheap overnight electricity.

 

[Chris94]

Thanks for your response!

it uses power from the EVSE (charge point) to warm up and maintain heat in the battery during the 3 hours before your departure time.

That's what was missing when I went for the test drive-- I think they charged up the car and let it sit. I have only just started looking at the options for off-peak charging for my other EV (a Chevrolet Bolt EUV). We only recently got a "smart meter" that can do that.
I'll have to test the preconditioning when I take the car home for a night-- hopefully the weather won't be a deal breaker when it comes to range.

 

[Chris94]

I brought the car home (4 mile drive with the battery indicating fully charged) and after sitting a while in may garage (roughly 32F/0C) while I familiarized myself with the car, I saw the range has increased from 56 miles to 84 miles on the battery (50 on the Rex side.) I set up battery conditioning with a planned drive away time of 10am (that's 14 hours away.) I plugged in the level 1 EVSE and the display showed a target of 96 miles for 10am. Next morning at 10am, the indicated range is 67 miles and the bars indicate the battery is "full."

So why does the range increase while NOT charging and decrease after charging for 14 hours? I know range estimation can't be exact, but these fluctuations make no sense to me. There is a big difference between 56 and 96, and even the 96 seems low for 28 kWh. My car's battery report suggests a range of 148 miles in my local winter conditions.

If anyone has any insights, I'd appreciate it.

 

[nickp]

The Rex is rated at a capacity of 97 miles when fully charged. Treat that as a baseline. Anything more or less will depend on your driving style, terrain, weather etc. Yes, cold weather will affect your range.

 

[Chris94]

Thanks. That range is battery only, not using the Rex?

 

[eNate]

Ignoring the chilly temperatures and cold-soaked battery for a moment, don't discount the fact that used cars are often driven hard and put away wet.

The i3 bases its range estimate on the last 15 or 18 miles of driving. If somebody is grinding it around the local streets surrounding the dealership, or doing jackrabbit starts on the freeway on ramp, that's all that's reflected in the guess-o-meter reading.

A half hour of sane driving will bring that figure into check, no matter the weather conditions.

My first i3, a 24,000 mile used 2017 BEV, displayed a similarly appalling range estimate when I took it out of the dealership lot in sunny San Jose CA.

You're right, kappa max isn't the end-all / be-all, but 28+ is a healthy looking value.

 

[Chris94]

Thanks for that perspective! I must remember to stop hyperventilating about range after 16 hours of ownership. Just drove 13 miles doing errands and the range dropped just 1 mile, while the rex range went up 6 miles. I will keep an eye on it and hopefully it will settle to something that reflects my "sane driving."

 

[Mondomensch]

While the range estimate is just an estimate, the battery percentage charge is pretty solid. You'll soon get a feel for how far you'll get with say 5% discharge for your driving style and climate conditions. As you get used to one pedal driving and almost never using the brakes (all Regen instead), you'll be pretty efficient unless you go at highway speeds.

 

[eNate]

While the range estimate is just an estimate, the battery percentage charge is pretty solid. You'll soon get a feel for how far you'll get with say 5% discharge for your driving style ...

Good points, and that reminds me, @Chris94 if you haven't done so already, drive the battery down into the single digits, then bring it up to 100% SOC, and maybe even try to leave it parked at a higher SOC for a few days (doesn't need to be continuously parked). The 0 to 100 charge will recalibrate the BMS to possibly provide a more accurate estimation of the battery SOC, and if there is any cell balancing that needs to happen it'll do that while the car is at rest, not charging, in the higher % range.