[EPedroza95]

I have a 2020 BMW M340i RWD and I got a message saying battery very low. My convenience features stopped working and my ambient lighting isn’t on when I turn on the car so I know if this charge doesn’t work I will have to replace the battery. I know there is a lithium ion battery under the hood and an AGM battery in the trunk. I purchased the CTEK battery charger and it has an AGM option. Do I have to charge both batteries separately in their own respective modes? I read somewhere to plug into the li-ion battery under the hood and use AGM mode but that doesn’t sound right to me. Would I use regular charging under the hood and then charge using AGM mode for the battery in the trunk separately? Any advice would help!

[pneumodoc]

Just charge the battery under the hood using the positive lead that’s there and the grounding point there. You dont have to select AGM mode (but I think that people disagree on that).

[G22b58]

Just to be clear. The dedicated charging/jump start posts under the hood are connected to the 12V battery in the trunk. Connect to these, and I'm convinced that the starter battery in the trunk is AGM so I would select that if the charger has that mode.

The car takes care of charging the "auxiliary" battery under the hood. (Assuming your 2020 model is not an MHEV, this would be a 12V (or 13V something) Lithium battery. For the MHEV models, this is a 44V Lithium)

[CanonEOS]

Or just drive the car in sport mode and manual shift and let it charge up after around 20 miles

[G22b58]

The starter battery (lead battery in the trunk) charges slowly at higher SoC, so might be better to charge overnight. If CanonEOS refers to the lithium battery, I agree. (At least in an MHEV, so assume it would be similar) that the lithium can be charged fast with some engine braking.

[EPedroza95]

Originally Posted by G22b58

Just to be clear. The dedicated charging/jump start posts under the hood are connected to the 12V battery in the trunk. Connect to these, and I'm convinced that the starter battery in the trunk is AGM so I would select that if the charger has that mode.

The car takes care of charging the "auxiliary" battery under the hood. (Assuming your 2020 model is not an MHEV, this would be a 12V (or 13V something) Lithium battery. For the MHEV models, this is a 44V Lithium)

Update : As I was waiting for the CTEK charger to arrive I drove the car around hoping it would charger the battery. Sure enough, my convenience features came back and everything seemed to return to normal. But then today I go to turn the car on and it will not Turn on. No engine lights no messages. I have it plugged in and going to leave it overnight, but I’m wondering if it has to do with that starter recall I got a week ago in the mail.

[Jasonk21]

Does the dash light up if you hit the start button, also does your car crank if you try to start it?