#bmw-i3

I am guessing that the OP eventually figured it out, but since no-one posted the correct answer here, and I just figured it out the hard way, I thought I would share what I learned. Like the OP, I could not get the disconnect slide to go back down until I realized that there is a latch clip on the left hand side that needs to be pulled out clear of the sliding part. In addition, the red tab at the top needs to be pulled up to its highest point (in case you pressed it down at all while getting the mechanism to reconnect). Once these two barriers were addressed, my sliding connector snapped back into place with ease.

AUX18L Auxiliary and Start/Stop Battery, by East Penn

good 12v battery replacement vid

We used the Remy 12V Battery AUX18L

In the US it's important to know that you can use the: Energizer TX24HL AGM Motorcycle and ATV 12V Battery​ as a replacement for the 12 volt. It costs $105 at Amazon. Its been working flawlessly since November of 2023. It may be important to note that in my 2014 the entire car went dead and I had to watch a YouTube to find the emergency hood pull. I had bought the car from a dealer in 2017 so my original 12 volt was between 7 and 9 years old. Absolutely amazing.

I’d caution slightly. This battery seems to be a different physical size than the OEM, and the terminals look different as well. I like this one, because it is a one for one replacement: https://remybattery.com/start-stop-aux18l-auxiliary-battery.html

I worked with Ohmmu to ensure that its LFP battery would work well with an i3. The i3 DC-DC converter's output voltage is ideal for an LFP battery. The 0.5V higher resting voltage of Ohmmu's LFP isn't a problem with an i3's 12V electronics because 12V components are designed work well with the 14.0+ output voltage of the DC-DC converter. The higher resting voltage and the much more flat voltage vs. charge level curve of a LFP battery means that the risk of all of the spurious DTC's being stored when the OEM battery's voltage drops too low when it fails isn't as great with a LFP battery. My Ohmmu LFP battery has been in our former 2019 and current 2021 i3's for about a year without any problems.

If your car still has its original 12 volt battery, your problems may be caused by a 12 volt battery failure. They tend to fail within 4 or 5 years, and, when they do, the car becomes completely inoperable.