Battery Replacement Under Warranty

[Oleksiy]

I just checked my I3 and it is showing 12.3 on kappa max. Does outside temperature affect this reading?

In my case low temperature seems to accelerate the rate of Batt.Kapa decrease. But the latter never picks up in summer. Check my stats here, I have a chart with Batt.Kapa over months later in the thread viewtopic.php?t=16253

[Oleksiy]

I'm curious if an easy way to check battery capacity more accurately is to just fast charge to known values a couple times and see how much kwh are able to be used. Or is this that wildly inaccurate? Isn't that what BMW is doing more or less when they discharge and then recharge (from what i think I remember reading).

My understanding is that Batt.Kapa shows the kWh that the battery is either able or allowed to accept during charging. At least that's been happening in my case (I checked this assumption many times, including after almost complete battery depletion and charging up to 100%).

As to the BMW battery capacity test procedure, I think it starts from the battery reset, then battery depletion and charging or vice versa. It's available in ISTA+, and there are people who tried it at home. I'm reluctant to since it's said to kill the 12v battery in the process.

[alohart]

I'm curious if an easy way to check battery capacity more accurately is to just fast charge to known values a couple times and see how much kwh are able to be used. Or is this that wildly inaccurate? Isn't that what BMW is doing more or less when they discharge and then recharge (from what i think I remember reading).

I've read that the i3's nominal battery capacity is determined by charging/discharging at a C/3 rate. That means for a 21.6 kWh battery pack (60 Ah), the charge/discharge power would be 21.6 kWh / 3 h = 7.2 kW. That's the maximum single-phase AC charging power, so measuring the kWh vended when AC charging at 7.2 kW would be a good start. However, the Idaho National Lab measured the AC charging efficiency as 93.8%, so the energy vended would need to be multiplied by 0.983 to calculate the energy added to the battery pack.

[CanisLupus]

I think that the one thing that's clear is if the battery is at or near the optimum temperature (~25C) during charging then it will show it's greatest capacity . Keeping it at that temperature for the duration of charging would require at least LEVEL 2 .

[Oleksiy]

Regardless of the ambient temperature and charging power the number of kWh the battery receives is equal to its current Batt.Kapa, taking into account 5-10% losses. That's according to my logs (daily for 20 months), but I don't think i3 battery packs are as unique as everything else these days, so I believe this should be true for all of them.

Given Batt.Kapa usually fluctuates 0.1-0.4 kWh from day to day, I assume this indicator simply shows the real amount of charge received during the previous session, extrapolated to 100% capacity.

Why Batt.Kapa and the available capacity decrease precipitously on some 60Ah cars is a totally different question. I'd be very interested to find out.

[panamamike]

An odd factoid. On another board several i3 owners experiencing noticeable range degradation said that after replacing their (aging) 12v battery and registering the new one, their range went back to near normal. One of the owners this happened to mentioned that when their Dealer was apprised, was told was some sort of GOM/ECU software glitch.

MKH, what do you mean by registering the new one? I have a 2015 i3 with a lower than expected Kappa that had the 12v replaced not too long ago. Wondering if I can try the registering to get the capacity to normal. The help would be appreciated.

[alohart]

MKH, what do you mean by registering the new one? I have a 2015 i3 with a lower than expected Kappa that had the 12v replaced not too long ago. Wondering if I can try the registering to get the capacity to normal.

Registering a new 12 V battery is telling the module responsible for charging the 12 V battery about the replacement battery including its type (e.g., AGM, flooded cell), capacity (e.g. 20 Ah), and replacement date. If the battery is the type and capacity of the original battery, only the replacement date need be registered. According to a BMW i mechanic, the replacement date tells a mechanic in the future when the battery was last replaced but doesn't do anything else. So registering a 12 V battery won't affect the usable capacity of the high-voltage battery pack.

[Bertone]

My 2017 i3 94Ah hidden menu shows Batt.Kapa max = 29,2 kWh. The car has 18.000 kms on the clock.

If true, I believe this is a good value since I've read that net battery capacity for a 94Ah is around 28,8 kWh...right?

[Kristis]

My 2017 i3 94Ah hidden menu shows Batt.Kapa max = 29,2 kWh. The car has 18.000 kms on the clock.

If true, I believe this is a good value since I've read that nominal battery capacity for a 94Ah is around 28,8 kWh...right?

Hard to tell, mine was reading 29.9 kw/h during summer and now it only shows 28.4 kw/h. Im currently at a bit lower than 39 000km But yeah, your numbers seem right

[JLB2]

Wow. 28kwh kappa max. I'm envious