I bought a used BMW i3 94 Ah. This is battery degradation after 3 years - battery replacement after 2039 :) [Reader]

BMW just boasted that they made 200 3 i2s. A car bought new is expensive, but in the secondary market you can find quite a few cars after a 5-year lease that have relatively low mileage and a good price. This is the model that our Reader chose - and now he decided to check the degradation of the battery in his copy.

The following text was compiled from materials sent to the editor and contains an editorial introduction about the BMW i3 versions.

Deteriorating battery life in a used BMW i3

Table of contents

• Deteriorating battery life in a used BMW i3
  • Battery destruction in BMW i3 - several different methods and calculations
  • Conclusion: degradation by 4-5 percent, battery replacement no earlier than 2040.

As a reminder: The BMW i3 is a class B / B-SUV vehicle, available in versions with cells with a capacity of 60, 94 and 120 Ah, that is, with batteries with a capacity of

• 19,4 (21,6) kWh - 60 Ah (first generation BMW i3),
• 27,2-29,9 (33,2) kWh - 94 Ah (facelift version),
• 37,5-39,8 (42,2) kWh - 120 Ah (option currently on sale).

The useful values ​​differ because the manufacturer does not provide them, and there is a lot of data coming from the market.

Specification of the Samsung SDI 94 Ah cell included in the BMW i3 battery. Find the units with errors 🙂 (c) Samsung SDI

Our reader chose the middle version with a ~ 29,9 (33,2) kWh battery, designated as 94 Ah. Today his car is 3 years old and has run over 100 kilometers..

> Used BMW i3 from Germany, or my path to electromobility - part 1/2 [Czytelnik Tomek]

Battery destruction in BMW i3 - several different methods and calculations

To check the drop in battery capacity, I need to know the nominal and current capacity. I know the first one (29,9 kWh), the second one I can test with several different methods.

Method No. 1. I fully charged the car and drove 210 kilometers using 92 percent of the energy. The average consumption was 12,6 kWh / 100 km (126 Wh / km), the average speed was 79 km / h. Since I drove 92 km on 210% battery, it would be 228,3 km on a full battery.

Based on this, it is easy to calculate that the available battery capacity is 28,76 kWh. It does 3,8 percent (1,14 kWh) or 9 kilometers loss of range.

Method # 2. This way is easier. Instead of driving, simply enter the BMW i3 service menu and check the status reported by the vehicle's BMS - battery management system. For me it is 28,3 kWh. Compared to factory data (29,9 kWh) lost 1,6 kWh, 5,4% power, which is approximately 12,7 km.

Method # 3. The third way is to use some kind of application that connects to the car via the OBD II interface. For BMW i3, this app is Electrified. The health status index (SOH) is 90 percent, suggesting that the car has lost 10 percent of its original capacity.

Where do these values ​​come from? Hard to say. Perhaps the application developer took the maximum values ​​as a starting point and added to the degradation a period of formation of a passivation layer (SEI), which cannot be avoided and which at first “eats up” even a few kilowatt-hours. ... From the technical characteristics of the elements (first illustration in the text), we can easily calculate that the maximum battery capacity of the BMW i3 is 96 cells x 95,6 Ah medium capacity x 4,15 V voltage at full charge = 38,1 kWh (!).

BMW gives only 33 kWh, because it uses a lower buffer (i.e. does not allow the cells to discharge to the end), and also remembers the process of creating a passivation layer.

> Total battery capacity and usable battery capacity - what is it about? [WE WILL ANSWER]

It may also be that capacity is taken into account in the SOH parameter of the Electrified application. Oraz uneven voltage on the cells. In other words, "state of health" does not mean individual "performance".

In any case, We reject the Electrified result as not very reliable.at least when assessing battery wear. However, we can take the capacity in Ah (90,7) seen in the appendix and refer it to the cell specification. Depending on whether we focus on the minimum capacity (94 Ah) or the average capacity (95,6 Ah), power loss was 3,5 or 5,1 percent.

Conclusion: degradation by 4-5 percent, battery replacement no earlier than 2040.

Our reliable measurements show that for 3 years of operation and with a mileage of 100 km battery degradation was about 4-5 percent... This gives about 10 kilometers less flight range every three years / 100. kilometers of run. I reach 65 percent of the original power - a threshold that is considered a high degree of degradation - when the car is 23 years old or 780 thousand kilometers.

After about 20 years. Then I will need to consider if I am replacing the battery, or maybe I will use a lower wattage and weaker range. 🙂

What does this exploitation look like? The machine is being treated normally, at home I charge it from a 230 V outlet or a wall charging station (11 kW). During the year I make several trips around Poland when I use DC fast charging stations (DC, up to 50 kW). This probably has nothing to do with decreasing battery capacity, but I like eco-driving and sometimes drop to an average of 12 kWh / 100 km (120 Wh / km) on trails.

After such a trip the next day, the car can predict a range of 261 km in Eco Pro mode:

Editor's note www.elektrowoz.pl: Normally processed lithium-ion cells usually age gradually (linearly). However, it can happen that one fails faster than the other, and then the BMS will actually report a problem with the battery. Fortunately, in such cases, it is enough to disassemble the battery and replace one damaged cell, which is much cheaper than replacing the entire battery.

Note 2 from www.elektrowoz.pl editorial office: here is a study of the capacity of cells used in the BMW i3 by the manufacturer of these cells, Samsung SDI. You can see that cells lose capacity linearly for at least the first 1,5k cycles. This is supported by the market data, and therefore we felt that the assumption of a linear decrease in capacity makes sense. The measured lifetime in 4 complete working cycles is in good agreement with the calculations of our reader:

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