BMW i3 auxiliary battery sizes

bwilson4web said:

I suspect the post-drive fans and cooling loops are driven by the 12V battery.

Click to expand...

jadnashuanh said:

You should be able to do it with the Bimmercode app, assuming you have iOS devices.

Click to expand...

tman66 said:

I'm going on vacation from Saturday to Saturday and was thinking of leaving the i3 plugged into the standard 110v wall charger while I'm gone. I have a 6:00am climatize schedule set for weekdays as well. The i3 will be in the garage with expected minus (Celcius) temps next week.

Would that be ok or is there a better way ?

Click to expand...

alohart said:

tman66 said:

I'm going on vacation from Saturday to Saturday and was thinking of leaving the i3 plugged into the standard 110v wall charger while I'm gone. I have a 6:00am climatize schedule set for weekdays as well. The i3 will be in the garage with expected minus (Celcius) temps next week.

Would that be ok or is there a better way ?

Click to expand...

Just park it with climatization off, the battery pack charge level ~50%, and the EVSE not plugged in. The 12 V battery won't discharge enough in 7 days to cause problems, the Li-ion battery pack won't discharge enough to be noticeable, and you won't waste energy climatizing a car that won't be driven.

Click to expand...

tman66 said:

Is there any particular reason why the battery should be at ~50% and not let’s say 100%?

Click to expand...

alohart said:

tman66 said:

Is there any particular reason why the battery should be at ~50% and not let’s say 100%?

Click to expand...

A Li-ion battery cell degrades more rapidly as its charge level varies from ~50% (i.e., more rapidly at very low or very high charge levels compared with mid-range charge levels). The i3's battery management system doesn't allow its cells to reach 0% or 100% charge levels to protect them from rapid degradation. According to the excellent book Electric Vehicles and the BMW i3 (60 Ah and 94 Ah) by David J. Bricknell, a 60 Ah battery pack can't be discharged lower than ~10% (a displayed charge level of 0%) or charged higher than ~95% (a displayed charge level of 100%). So if a battery pack is allowed to remain at a displayed charge level of 100%, the actual 95% charge level is still quite high and results in cells degrading more rapidly than at lower charge levels.

Many of us who plan to keep our i3's past the battery pack warranty period do what we can to minimize the inevitable battery cell degradation rate. Minimizing the time a battery pack is allowed to remain at a high charge level is one of these strategies.

For those leasing an i3 or who don't plan to keep their i3's for many years might feel that manually managing the battery pack's charge level is more trouble than they want to endure, so they just leave their EVSE's plugged in to their i3's whenever they're parked at home.

Click to expand...

EVMan said:

BMW is running the Chargeforward program in some places in US, and it encourages to charge to 100% every time , and when ever possible.
Most people are the Lease , so they could also care less .

Click to expand...

Bawareca said:

jadnashuanh said:

The charging routine for an AGM battery is different than one for a typical lead-acid battery. When BMW sweated every gram of weight on the car's design, there obviously were some compromises, but the vast majority of people get by fine with the stock battery. That new battery may not have the same life since an AGM typically uses a slightly higher charging voltage that would shorten the life of a typical one. On some BMW models, you can adjust the charging routine depending on the battery installed, but I do not know if they are accessible with the right software on the i3.

Click to expand...

My car came with a completely dead battery and that upset me a bit (10k miles). Browsing REaloem I found the upgraded 40Ah battery and instead of buying another laptop battery (the original one ), I bought the upgraded without doing much research. At the end I had to modify the battery tray and I had to change the position of the windshield washer reservoir.
There has been many cases when the main battery shuts down completely at low state of charge and the small "laptop" battery will be sufficient for only a few minutes before it is completely exhausted, let alone to start the REX. The 40ah battery has some real energy stored in it and if one needs it only 1 time it is worth it (for me).
From what I see there is no "charge routine". The moment the car wakes-up 14-14.5V from the main battery thru the DC/DC inverter is supplied to the 12V system, to the moment the car goes to "sleep". Actually the original AGM battery is very fragile when fully discharged (partially because of the low capacity), lead battery should fare much better in these conditions.

Click to expand...

• Pulse (5-second) Hot Cranking Amps (PHCA): 520
• Cold Cranking Amps (CCA): 170
• 20Hr Nominal Capacity (Ah): 16
• Reserve Capacity Minutes: 24
• Dimensions L x W x H (in): 7.15 x 3.00 x 6.65
• Metric Dimensions L x W x H (mm): 181.5 x 76.3 x 167.8
• Weight (lbs): 15.4
• Weight (kg): 7

jreynaert said:

I like the "Lifetime" warranty on this from FCP Euro!
https://www.fcpeuro.com/products/powersport-battery-odyssey-pc680
Probably going to give this a try, when my battery starts to go!

• Pulse (5-second) Hot Cranking Amps (PHCA): 520
• Cold Cranking Amps (CCA): 170
• 20Hr Nominal Capacity (Ah): 16
• Reserve Capacity Minutes: 24
• Dimensions L x W x H (in): 7.15 x 3.00 x 6.65
• Metric Dimensions L x W x H (mm): 181.5 x 76.3 x 167.8
• Weight (lbs): 15.4
• Weight (kg): 7

Click to expand...

alohart said:

I had good experience with Odyssey batteries during our 15-year ownership of a G1 Honda Insight hybrid. However the PC680 that interests you has only 16 Ah capacity which is considerably less than the 20 Ah capacity of the OEM AUX18L battery. This might not be a significant problem because the DC-DC converter is on much of the time providing almost unlimited 12 V power from the HV battery. To the extent that the i3's automatic 12 V battery maintenance is reliable, even when the 12 V battery's charge level decreases, it would be automatically charged for an hour to increase the charge level. However, with a lower capacity, automatic 12 V battery maintenance might have to occur more frequently or might not work well enough to increase the charge level sufficiently. There's probably a good reason why BMW didn't install a lower capacity 12 V battery.

The PC680 is a power sports battery without a common vent like the AUX18L. It is not meant to be mounted in an enclosed space. When it fails, if it emits flammable, poisonous gasses, these gasses could accumulate in the frunk rather than being routed to the right front fender well as is done with the AUX18L. The frunk certainly isn't airtight, so this probably isn't a significant problem. However, BMW felt that venting battery gasses to the wheel well was important enough that they installed a battery that supported this venting.

Another problem with the PC680 might be its 0.27" (6 mm) greater height than the AUX18L battery. I've had to deal with this problem because the LFP battery that I installed is 0.38" (10 mm) taller than the AUX18L. You would probably have to move the 0.25" (6 mm) thick pad on the underside of the horizontal section of the battery hold-down bracket to the inside of the vertical section to lower the hold-down bracket enough so that its top attachment screw can be screwed into its nut and to limit how much the 0.56" (13 mm) thinner could move around. Attaching spacers to the side of the battery would help secure it. The screw-on SAE posts from the AUX18L battery probably wouldn't fit a PC680 securely, so you'd probably need to purchase screw-on SAE posts designed for the PC680.

I suggest investigating LFP batteries as AUX18L replacements. If you live where winter temperatures could be low, you'd probably want to avoid LFP batteries without automatic internal battery heaters. Tesla no longer installs AGM 12 V batteries in its vehicles instead installing lithium chemistry batteries, so this is probably the future for 12 V batteries.

Click to expand...