Crowdsourcing information - I will be traveling for ~3 weeks, longest trip since getting my ‘23 SE. Is it necessary (or recommended) to hook up a battery maintainer (for example the NOCO genius model) for the 12V battery? The owners manual recommends not leaving the EV charger plugged in or the high voltage battery fully charged for long periods , but I do not see any recommendations for the 12V battery. For ICE cars I have used a battery maintainer for trips longer than 2 weeks, especially in the winter.
Unlike the the complaining I read on InsideEVs' Hyundai/Kia forums, no one on this forum who hasn't installed extra electronics (eg. traffic cams, OBDII dongle) has complained about parasitic battery draining in their SE. I've made it 2 weeks without problem, but never tried to stretch it to 3. If you decide to wing it, please report how it turns out.
the car will maintain the low-voltage battery itself. No need to hook anything up. If you read the 2023 owners manual, it quite clearly says to park the vehicle with a 30 to 50% state of charge, and check it after six months.
I've left my SE at 100% SoC and unplugged for five days now, while on a train excursion halfway across the country. I will not be home for another six days, but right now the app is showing my SE is still at 100% SoC and I'm sure the 12 V battery is not doing anything. But the SE does automatically keep the 12 V battery charged from the high-voltage batteries, so no maintainer is needed. (Note the 2021 SE owner's manual says to leave it unplugged at 100% SoC for up to three months. I don't exactly trust the manual to be very accurate, I think it's been corrupted by BMW guidance pasted into MINI documents. Case in point: the ridiculous charge-to-80% language.)
I have left our 2021 SE (2022 in the US) for 4 weeks at 100% SOC, unplugged. While monitoring it with app, it was 100% SOC, and when we arrived it was still 100% SOC and 100% SOH, and it started fine and was zippy on the curves in the hills.
Has MINI verified the traction battery will charge the 12-Volt battery when the SE is not powered up? If so, I wonder if there's a limit to how long this sacrifice will continue?
I believe it's explicitly stated in the Motorer's Guide, near the warning about the car being unable to start with a dead 12 V battery. I know from my battery discharging fault issue (caused by pocket-pressed fob button "waking" my SE up) that the SE automatically keeps the 12 V battery charged as long as there's juice in the high-voltage batteries.
Your experience appears to indicate the traction battery charges the 12-Volt battery even when the SE is not powered on, but I couldn't verify it in this part of the Motorer's Guide: The Owners Manual repeats those two paragraphs and also has this info:
