Earlier this evening, I was leaving for work when I encountered a completely dead 2014 BMW i3. I know from reading the i3 forum that it HAD to be the 12v battery. I called for roadside assistance and listed my car as a “hybrid“ because I do have the gas-powered range extender. While I waited for the tech to arrive, I disengaged the high voltage battery, as I had read about this multiple times on the i3 forum. When the tech got to my house, I told him that I had made the disconnect, and he said that we needed to reconnect it, or the charge wouldn’t “work.” I was skeptical, but I agreed, and we reconnected the 12v to the HV. Prior to the “jump,” my HV battery was charged to 100%. After he hit the 12v with his battery pack, my HV percentage wouldn’t even show up on the screen. My Rex percentage showed up, but not the HV. Is it possible that the ultra high voltage from his battery pack knocked the charge out of my HV? Could it have done more extensive damage? (Dear God, I hope not!) The car would only stay on for a few seconds, and then shut off again. So, I plugged the car back in to charge the HV, and I ordered a trickle charger to put on the 12v again tomorrow.
I’m just looking for someone to reassure me that there is some sort of safewall that would not allow my HV to be “overcharged“. The 12v doesn’t feed the HV directly, correct? Like, that massive current wouldn’t travel from the 12v through to the HV? This is a 2014, so my highest charging level is two. I should have insisted that we at least try the jump without the batteries connected, but I didn’t want to be contrary.
Please tell me I didn’t kill my perfect car….
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bro, take the car to a dealer, we’re not tesla, we can’t diagnose your 9-year-old ev’s issues over the internet
Lol my dealer isn’t an expert either. They have ONE roaming dude for the entire province, and you have to book him and wait for him to grace your car with his presence.
have you tried turning it off and on again?
how about rice? have you put it in rice?
maybe pull the connector out and blow in it realll good… side to side… blow and clean it out.
if that dont fix it… yeah you fried some electrical component by having the hv connected when those who knew better said to not to. im sure itll cost a fortune being a bmw and 10 years old to replace whatever circuit board got cooked.
but the only way to actually know… take it to the dealer.
Let me start by saying I’m not an expert on the specifics of your vehicle. But Your HV was most likely not engaged. EVs default in a state of HV open circuit (contactors open) and it’s extremely difficult to force it to close the circuit with all of the software safeguards in place. It seems like there’s something wrong on your 12v system which is sending error messages preventing the car from starting. That being said, it’s extremely foolish to jump an EV 12v battery rather than replace it. it’s function is akin to a backup battery in a PC or those old school calculators with a AA plus coin battery, you know? If it were dying, you’d probably notice behavior earlier. They aren’t used to start cars any more, but to keep them alive. Anyway, take it to an expert. Not a general tech or roadside service. Either the OEM service center or somebody with proven success on your vehicle. EVs are not yet at a place where the common Joe schmo can try to service themselves. This is proven by your experience and the lack of understanding in the tech. Good luck!
Have had to jump an EV several times what with the Kia I had around COVID time mixed with not driving anywhere leading to frequent flat 12v battery. Jumping a EV is both normal and described in the manual, and a flat 12v as a one off does not indicate it needs replacing.
Yes the 12V doesn’t charge the HV battery, it’s the other way around with the HV battery charging the 12V battery like an alternator does. A 12V jumper box would not be capable of overcharging a 400V battery.
After disconnecting the battery and the 12V battery being dead it likely needed time to calibrate the BMS to come up with the correct SOC so it showed blank. And usually you only disconnect the HV battery when your servicing the HV system or the car has been in an accident.
Jumpstarting a car isn’t like shocking someone’s chest with a defibrillator. There is no massive current. The mobile ones are just a smaller 12V battery that will provide enough juice for your car to turn on in place of your flat 12V battery. Once the car is on, it takes over the job of charging the flat battery so the jumpstarter battery can be removed. You can’t jumpstart an EV with the HV service disconnect pulled, because your whole goal is to get enough power from the jumpstarter’s battery to pass the car’s startup self-checks that happen before the HV battery is engaged and takes over.
When’s the last time you replaced the 12 volt battery? In 2014 nobody was fooling around with lithium 12-volt packs, they were just using bog-standard lead acid batteries If it’s more than 5 years old, it’s probably done.
And if you’re wondering why there is so much public anxiety about EV battery life, this is why. Everyone over 30 has had to replace an ICE car battery at least once. People just assume EV battries are made of the same stuff.