Installed my new 12V battery yesterday

[Jim0el]

Having seen many posts here regarding the 12V battery and the symptoms of its failure, I recognized when mine was going (including rapid drop in my e-range) ... and I didn't get stranded! I bought one online, that I could pick up just 15 miles away. Well, the item I ordered turned out to be a bargain (which I always favor), but the thing had weird connection posts, so I returned it. No other business in the area could offer what I needed, so I broke down and went to the BMW dealer. I was expecting a price around $150 (whereas the online purchase had been $98). Well, the dealer had one in stock, and the price quoted was almost $300. I argued and whined and complained and went on and on, and the price was finally dropped to $200.

Before dark, I had it installed. I followed closely the YouTube procedure posted by LavaLabs. His car was a 2014, with a very different HV disconnect than I found on my 2017, but I figured mine out: pry out the locking tab on the left, pull up the red tab, then use that tab (by pressing it back) to release the body of the disconnect. Otherwise, the swap was straightforward, and I'm back on the road again!

 

[alohart]

Having seen many posts here regarding the 12V battery and the symptoms of its failure, I recognized when mine was going (including rapid drop in my e-range)

I didn't experience a rapid decrease in the predicted range when the 12V batteries in 2 previous i3's were failing. Please explain in more detail what you experienced. The displayed charge level of a local 2014 i3 is decreasing considerably overnight with no stored diagnostic trouble codes (DTC's). Even though the 12V battery was replaced within the past year, I wonder whether it might be defective even though everything that depends on the 12V battery seems to be working normally.

I bought one online, that I could pick up just 15 miles away. Well, the item I ordered turned out to be a bargain (which I always favor), but the thing had weird connection posts, so I returned it.

Sounds like a power sports battery. It could have been used by modifying the screw-on posts from the original battery so that they would fit properly. However, it doesn't have a vent tube connector which might be a minor difference.

No other business in the area could offer what I needed, so I broke down and went to the BMW dealer. I was expecting a price around $150 (whereas the online purchase had been $98). Well, the dealer had one in stock, and the price quoted was almost $300. I argued and whined and complained and went on and on, and the price was finally dropped to $200.

~$200 is what our local BMW charges. What a rip-off attempt to get $300.

Before dark, I had it installed.

Did you charge it before installing it? A local i3 owner bought a 12V battery from our local BMW dealer and discovered that its voltage was only ~12.3V which corresponds to a pretty low charge level that might have caused problems.

 

[Jim0el]

I didn't experience a rapid decrease in the predicted range when the 12V batteries in 2 previous i3's were failing. Please explain in more detail what you experienced. The displayed charge level of a local 2014 i3 is decreasing considerably overnight with no stored diagnostic trouble codes (DTC's). Even though the 12V battery was replaced within the past year, I wonder whether it might be defective even though everything that depends on the 12V battery seems to be working normally.

Sounds like a power sports battery. It could have been used by modifying the screw-on posts from the original battery so that they would fit properly. However, it doesn't have a vent tube connector which might be a minor difference.

~$200 is what our local BMW charges. What a rip-off attempt to get $300.

Did you charge it before installing it? A local i3 owner bought a 12V battery from our local BMW dealer and discovered that its voltage was only ~12.3V which corresponds to a pretty low charge level that might have caused problems.

Yes, Alohart, I first had a failure of the fob to unlock the door by proximity, though pressing the unlock button did work; then the radio wouldn't go on, and there was a brief notice "Unable to charge." The car worked fine the rest of the day, and I charged the HV battery to about 80%. Overnight, the charge had dropped to 60-some %, but I didn't use the car. That's when I went online to buy a replacement battery.

The next morning I got another brief flash of the "Unable to charge" notice and my HV battery was down to about 35%, but everything seemed to be working fine. I drove the 15 miles to pick up that new battery and found that it had different connectors. Yes, I later figured out that I probably could have mounted the BMW connectors anyway, but the new "power sports" battery was only rated for 18 Ah, not 20, so the strange posts were enough justification to return it. And yes, it also lacked the vent. One auto parts shop could have ordered the stock battery for me, but warned that the holidays would probable cause a shipping delay. Not wanting to do all my driving in the diesel pickup 'til January, I opted to go to the dealer.

No, I didn't charge the battery before installing it, but got a hefty spark during installation, so I figured it would work. Sure enough, all I had to do was reset time and date, and all is well. My zeroed trip meter tells me how far I've gone since the swap. I did charge to 87% late yesterday, and now a day later it's still at 87%, so my worries are relieved.

Yes, if your local '14 is losing e-range overnight, I'd suspect that the 12V battery isn't holding a charge. Since it was replaced recently, maybe it's just a loose or corroded clamp?

 

[alohart]

Yes, if your local '14 is losing e-range overnight, I'd suspect that the 12V battery isn't holding a charge. Since it was replaced recently, maybe it's just a loose or corroded clamp?

Both the cable clamps and screw-on posts were tight. However, even a relatively new battery could be failing. Unfortunately, there are no other symptoms that are typical with a failing 12V battery although when I measured its resting voltage, it was low. However, the car hasn't been driven much during the past few weeks, so the 12V battery could be discharged from a lack of sufficient driving.

 

[Jim0el]

Both the cable clamps and screw-on posts were tight. However, even a relatively new battery could be failing. Unfortunately, there are no other symptoms that are typical with a failing 12V battery although when I measured its resting voltage, it was low. However, the car hasn't been driven much during the past few weeks, so the 12V battery could be discharged from a lack of sufficient driving.

My understanding is that the HV battery will automatically top off the 12V battery, even when the vehicle isn't in use. Do you know otherwise? If the 12V is failing, though, it'll draw down the HV battery without benefit ....

 

[alohart]

My understanding is that the HV battery will automatically top off the 12V battery, even when the vehicle isn't in use. Do you know otherwise? If the 12V is failing, though, it'll draw down the HV battery without benefit ....

That's true. My 12V system logger recorded this happening when my 12V battery was failing. However, it is charged for only 1 hour until the 12V battery's voltage decreases again to some unknown level (12.50V for our i3, but others have reported 12.00V). This occurred only 4 times overnight before automatic 12V battery charging gave up, so the HV battery pack's charge level shouldn't have decreased much. The total capacity of the 12V battery is only 0.24 kWh (12V * 20 Ah / 1000 W/kW) which is a tiny percentage of the HV battery pack's usable capacity. I don't know how much power is consumed by the HV electronic modules when they are running, but that would add to the decrease of the HV battery pack's charge level. However, I didn't notice the HV battery pack charge level decreasing when this was occurring. Of course, with a 120 Ah battery pack, any decrease would be less than half that of a somewhat degraded 60 Ah battery pack, so maybe I just didn't notice.

 

[Jim0el]

That's true. My 12V system logger recorded this happening when my 12V battery was failing. However, it is charged for only 1 hour until the 12V battery's voltage decreases again to some unknown level (12.50V for our i3, but others have reported 12.00V). This occurred only 4 times overnight before automatic 12V battery charging gave up, so the HV battery pack's charge level shouldn't have decreased much. The total capacity of the 12V battery is only 0.24 kWh (12V * 20 Ah / 1000 W/kW) which is a tiny percentage of the HV battery pack's usable capacity. I don't know how much power is consumed by the HV electronic modules when they are running, but that would add to the decrease of the HV battery pack's charge level. However, I didn't notice the HV battery pack charge level decreasing when this was occurring. Of course, with a 120 Ah battery pack, any decrease would be less than half that of a somewhat degraded 60 Ah battery pack, so maybe I just didn't notice.

My 2017 REx has the 94Ah battery, so the drop would be more noticeable on mine than yours. My thinking was that aside from the inefficient charging (putting extended load on the HV battery), there may be multiple cycles of the attempt, which might take a lot of energy too.