[RClementTX]

Thanks "TheNew3" for your input.

I'm still at the "not so sure I know what's going on" stage after talking to BMW tech and doing some reading on Li Ion battery technology. BMW tech showed me the CTEK designed BMW charger that they use on showroom cars - it has lead acid and separate LiFePO4 charge profiles that are quite different in terms of voltage, bulk and saturation charge times/current levels, etc. They advise that they keep showroom cars on the charger on the LiFePO4 profile. So based on that, I bought their charger and put it on the X7 in LiFePO4 mode. I could not find a comparable CTEK charger that had both Lead Acid and LeFePO4 profiles ... so I'm presuming that there's enough going on here in our BMW mild hybrid system that using old CTEK MUS4.3 might be like playing with fire.

I let new charger "cook" for 12 hours and found a "power management" error message on the check control toward the end of that time. And as the charging progressed I noticed repeated relay action under the hood and in the vicinity of the LiFePO4 battery tucked up under the hood on the passenger/firewall side. Also monitored voltages on the jump start terminals and found that they didn't show predictable voltage rise that I expected.

After studying Li Ion batteries tonight on the BatteryUniversity.Com site I now recognize that what's normal and good on a Lead Acid or AGM battery is not necessarily good on a Li Ion battery. (e.g. ... They don't want/like to be kept at full charge; any overcharging is death; charge rates are very critical.). So I have a note back into my BMW tech to ask for guidance regarding the 'power management' message and the clicking relays.

If we have any battery / 48V mild hybrid gurus on this forum, we could really use a crash course on the BMW system. I've searched for Tech Guides on the system and none appear to be posted/available.

All input/thoughts welcome. As I learn more from my techs, I'll post accordingly.

[Eternalthinker]

I will be leaving the country for several weeks and the only car I have that does not have a trickle charger is the X7. To make sure the battery does not go flat, should I have it connected to the battery in the trunk or the Lithium batter under the hood? Thank you

[jmciver]

Originally Posted by Eternalthinker

I will be leaving the country for several weeks and the only car I have that does not have a trickle charger is the X7. To make sure the battery does not go flat, should I have it connected to the battery in the trunk or the Lithium batter under the hood? Thank you

Use the battery terminals under the hood - that is what they are there for. The aux lithium battery in the engine compartment will be charged via the terminals under the hood if necessary.

[Eternalthinker]

Originally Posted by jmciver

Use the battery terminals under the hood - that is what they are there for. The aux lithium battery in the engine compartment will be charged via the terminals under the hood if necessary.

Thank you!

[sahileX7]

Originally Posted by ducatiti

Still new to my X7 and browsing this forum every night, just found out it has three batteries, one being a lithium ion. I have a CTEK charger with an AGM option. Do I have to use this AGM option? Would it hurt the battery to use a cheap trickle charger?

I’m new to my 2023 X7 as well and perusing this communities threads a lot, came across this albeit old thread. I’m using a CTEK charger as well in AGM mode but I basically spent the time to hook a CTEK quick connect outlet to the trunk battery directly. So when I want to charge I just plug it directly from the trunk. Has anyone done that? Is that not advisable or worst yet would that impact warranty?

[BobsM3Coupe]

Originally Posted by sahileX7

I’m new to my 2023 X7 as well and perusing this communities threads a lot, came across this albeit old thread. I’m using a CTEK charger as well in AGM mode but I basically spent the time to hook a CTEK quick connect outlet to the trunk battery directly. So when I want to charge I just plug it directly from the trunk. Has anyone done that? Is that not advisable or worst yet would that impact warranty?

It is not advisable. Even says so right in the most unread book in the world, the vehicle owners manual.

[sahileX7]

Originally Posted by BobsM3Coupe

It is not advisable. Even says so right in the most unread book in the world, the vehicle owners manual.

LOL, got it!

[sahileX7]

Although BMW Brunei but when researching CTEK comfort connect and BMW came across this link, looks like BMW themselves sell the comfort connector which looks exactly the same as the CTEK connector as others have pointed they may be the OEM manufacturer.

https://www.bmw.com.bn/en/topics/off...or-eyelet.html

[Qsilver7]

Originally Posted by BobsM3Coupe

It is not advisable. Even says so right in the most unread book in the world, the vehicle owners manual.

Originally Posted by sahileX7

LOL, got it!

Ditto BobsM3Coupe...its not advisable because hooking directly to the battery skips the IBS (intelligent battery sensor). So if there is a significant change in the battery's charge...this could cause warnings from the check control system since the IBS was not aware of the change to the battery.

Also, do not use the 12v (cig lighter) sockets to charge the battery either.

[sahileX7]

Originally Posted by Qsilver7

Ditto BobsM3Coupe...its not advisable because hooking directly to the battery skips the IBS (intelligent battery sensor). So if there is a significant change in the battery's charge...this could cause warnings from the check control system since the IBS was not aware of the change to the battery.

Also, do not use the 12v (cig lighter) sockets to charge the battery either.

Thank you! Net net I should take the connector off or at least never use it again...

[nicboy]

If I disconnect the main terminal cable, will that help preserve the battery as I'm going to park the car for a month. There is no power outlet in our community garage so cannot use a wall charger.

[thenew3]

Originally Posted by nicboy

If I disconnect the main terminal cable, will that help preserve the battery as I'm going to park the car for a month. There is no power outlet in our community garage so cannot use a wall charger.

One month is not a big deal. I've gone 2 months without driving the car and the battery was still fine.

If you can park outdoors under the sun, you can get a solar battery tender like the one listed below.

https://www.amazon.com/Upgraded-Wate...2s9dHJ1ZQ&th=1

[Orient330iNYC]

For the vehicles with the 48v battery, theres a tis bulletin that says the 48v battery is not charged if a charger smaller than 20a is connected and/or the hood is closed.
https://www.google.com/url?sa=t&sour...B9X3pd2k0Htg1O

[thenew3]

Originally Posted by Orient330iNYC

For the vehicles with the 48v battery, theres a tis bulletin that says the 48v battery is not charged if a charger smaller than 20a is connected and/or the hood is closed.
https://www.google.com/url?sa=t&sour...B9X3pd2k0Htg1O

That document also says
"Trickle chargers (< 20-amp output) or solar chargers will not be able to charge the 48 V battery, but could prevent further discharge to the 48 V battery when the 12 V battery is properly maintained to optimal SOC."

Which suggest that if you keep the 12V battery charged, the 48v should not discharge. So if that's the case, a solar or trickle charger on the 12V system should keep the 12V "maintained to optimal SOC" at which point the 48v should not discharge.

[25X740i]

I just ordered a 2025 X7 40i, my first BMW. This will be a second vehicle used mostly weekends and special occasions, so will commonly sit several days at a time. Coming from Lincoln Navigator, I know the heavy electronics can drain the battery when not driven for several days. Experience has taught me the importance of using a battery maintainer. With the Lincoln I just wired it directly to the battery. I understand from this thread that I need to utilize the “jump start” posts under the hood. Have also seen on another thread that hood must be closed and vehicle locked for battery maintainer to perform properly. Can anyone confirm or disprove this, or have any other advise to insure success?

[AvGeek]

Originally Posted by 25X740i

I just ordered a 2025 X7 40i, my first BMW. This will be a second vehicle used mostly weekends and special occasions, so will commonly sit several days at a time. Coming from Lincoln Navigator, I know the heavy electronics can drain the battery when not driven for several days. Experience has taught me the importance of using a battery maintainer. With the Lincoln I just wired it directly to the battery. I understand from this thread that I need to utilize the “jump start” posts under the hood. Have also seen on another thread that hood must be closed and vehicle locked for battery maintainer to perform properly. Can anyone confirm or disprove this, or have any other advise to insure success?

It's actually the opposite, do NOT close your hood when charging on a mild hybrid.

[25X740i]

Thanks! That part didn’t sound right to me! Makes sense to leave the hood open. Appreciate the advice. Can anyone confirm the part about the vehicle needing to be locked?

[Orient330iNYC]

Originally Posted by 25X740i

Thanks! That part didn’t sound right to me! Makes sense to leave the hood open. Appreciate the advice. Can anyone confirm the part about the vehicle needing to be locked?

locking the vehicle lets it enter sleep mode sooner. you can charge with the doors unlocked, but when the car is awake theres a fairly large draw on the battery.

[25X740i]

Thanks again! That explains it!