[sjb993]

Further to the recent lengthy post on the problems with battery charging for MHT cars, I'd be grateful for some advice.

If I were to disconnect the 12 volt battery completely and charge the battery by directly connecting the charger to the battery posts, what are the downsides?

TIA

[Soul_Glo]

Zero downsides but some annoyances.

Your car would see this as a hard reset once battery is disconnected for over 15 minutes. Loads of fault codes will flash up on the iDrive once reconnected. The good news is that all of these disappear within 10 miles of driving and even minutes. However, sometimes and very rarely a hard code might register and you would need to clear this using a scanner.

Obviously a secure garage is required and the car will need to be left unlocked with trunk open.

Personally, and correct me if I am wrong HighlandPete, I think the advice is to charge via dedicated points due to the invention of smart chargers with a reconditioning mode. I fail to see how a 12v regulated charger such as CTEK could blow up the intelligent battery sensor (IBS). Whereas, using the reconditioning mode with battery connected would send a series of higher voltage spikes to the battery and easily toast the IBS. Or simply disconnect the IBS if worried.

I have charged many BMW’s by connecting to the battery whilst the battery has been connected.

[sjb993]

Thanks Soul_Glo.

The car will be in my garage during charging. I have Bimmerlink so I assume I could clear errors with that

I did wonder whether any/all of my “personalisation settings” would be lost. Having said that, given that, if you were replacing the battery with a new one, you would need to register the new battery to clear the old battery’s status, some data is obviously maintained during disconnection - maybe in an SRAM or other memory.

[Beemer5to3]

Yep exactly as Soul_Glo has said, there’s a part of the battery positive lead that directly feeds all the modules in the car - that’s the main reason you can’t jump / charge the battery directly to the battery itself as you risk frying the modules.

[HighlandPete]

Originally Posted by Soul_Glo

Personally, and correct me if I am wrong HighlandPete, I think the advice is to charge via dedicated points due to the invention of smart chargers with a reconditioning mode. I fail to see how a 12v regulated charger such as CTEK could blow up the intelligent battery sensor (IBS). Whereas, using the reconditioning mode with battery connected would send a series of higher voltage spikes to the battery and easily toast the IBS. Or simply disconnect the IBS if worried.

I have charged many BMW’s by connecting to the battery whilst the battery has been connected.

If the battery is installed, BMW definitely instruct to use the terminals under the hood (bonnet). Only then does it ensure the charging is recognised by the vehicle electronics, in vehicles with an IBS.

It is not recommended to use the AGM 'recon' mode, as the voltage is too high. AGM mode is within spec' of 14.8V maximum.

[sjb993]

Originally Posted by HighlandPete

If the battery is installed, BMW definitely instruct to use the terminals under the hood (bonnet). Only then does it ensure the charging is recognised by the vehicle electronics, in vehicles with an IBS.

It is not recommended to use the AGM 'recon' mode, as the voltage is too high. AGM mode is within spec' of 14.8V maximum.

I don't have the technical knowledge to disagree with what you said. However, I'm pretty sure that in all the posts on this subject that I have read nobody, including myself, with an MHT car has succeeded in charging their battery via the connection points under the bonnet.

As far as I can tell, there is no alternative to disconnecting the battery and using the battery connection posts.

If, as is possible, I missed an alternative solution in the myriad of posts, I'd be very grateful if you would let me know where to find it.

TIA

[Seaford]

Originally Posted by sjb993

I don't have the technical knowledge to disagree with what you said. However, I'm pretty sure that in all the posts on this subject that I have read nobody, including myself, with an MHT car has succeeded in charging their battery via the connection points under the bonnet.

As far as I can tell, there is no alternative to disconnecting the battery and using the battery connection posts.

If, as is possible, I missed an alternative solution in the myriad of posts, I'd be very grateful if you would let me know where to find it.

TIA

Not being funny and I learned many years ago that there is no such thing as a stupid question….what does the handbook say on the subject - if anything?

[sjb993]

Originally Posted by Seaford

Not being funny and I learned many years ago that there is no such thing as a stupid question….what does the handbook say on the subject - if anything?

It’s really helpful.

[HighlandPete]

Originally Posted by sjb993

If, as is possible, I missed an alternative solution in the myriad of posts, I'd be very grateful if you would let me know where to find it. TIA

There does appear to be issues with some users not succeeding with charging the 12V battery. It is not clear why.

[Seaford]

Originally Posted by sjb993

It’s really helpful.

Nobody believed me at the time….my 330i (non hybrid) would only charge with the bonnet fully closed….have you tried that?

Please bear in mind I have no idea what ‘with the flap open’ means or knowledge of the 48v system when considering this post.

[sjb993]

Originally Posted by Seaford

Nobody believed me at the time….my 330i (non hybrid) would only charge with the bonnet fully closed….have you tried that?

Please bear in mind I have no idea what ‘with the flap open’ means or knowledge of the 48v system when considering this post.

For my first unsuccessful attempt I did have the bonnet closed. It was pointed out to me on here that I should have the bonnet open as this deactivates the 48V system. My second attempt with the bonnet open was also unsuccesful.

I have no idea what "flap open" means either.

[paulockenden]

Originally Posted by sjb993

I have no idea what "flap open" means either.

Bonnet flap.

[Seaford]

I suspect I know what ‘flap open’ means but if I went into detail I suspect I may get banned from here….

[TuffLittleUnit]

Originally Posted by Seaford

I suspect I know what ‘flap open’ means but if I went into detail I suspect I may get banned from here….

Why not just Google it ... from work?

[tyranniux]

I bought a ctek charger recently on advice from the other thread. Connected charger, closed bonnet fully and set to AGM recondition mode. Charged to 100% without issue.

I suspect the bonnet flap open is referring to the motorised grille which only opens when the car is upto temp. I wouldnt really want to leave the charger under the bonnet with the heat from the turbo sat right next to it, if nothing else but to avoid the temperature compensation from the charger being significantly off. I didnt experience any issues with the flaps being closed on a cold car.

[sjb993]

Tyranniux, the problems are confined to cars with Mild Hybrid Technology e.g. M340i. These cars have two batteries, 48v and 12v, and the bonnet has to be open in order to deactivate the 48v.

[tyranniux]

I have m340i mhev, charger reported successfully charged battery, no warnings in car or otherwise, bonnet closed etc

[sjb993]

Sorry, your details sidebar shows a 520i G30.

Have you checked the state of charge in the 12v battery? My charger also shows a fully charged battery, but when I checked the state of charge showed only 48%.

The "flap" actually is the bonnet and the battery won't charge with it open. FWIW, the only person I've come across when looking for information on this issue who has succeeded in charging their battery used a 25 amp charger.

[tyranniux]

Where does the SOC from the 12v battery appear?

Totally forgot I hadn't updated my profile, had the g21 over a year and the g30 been gone 6 months 😂

[sjb993]

I use the Bimmerlink App to read the SoC.

[Azure350z]

This could be irrelevant but could also be something to do with software and be relevant.

I have a 330i, non MHT.

I used a Ctek mxs5. 0 to charge the battery on Saturday night with the bonnet closed. The charger showed it charged fully. I then did around 60 miles of driving on Sunday for around an hour and a half.

I checked the battery soc today and it was only 55%. So I plugged the ctek back on and charged again but with the bonnet open until the charger said it was complete. I then checked the soc before even starting the car and it was only at 65%.

Now this is my first bmw and the battery is now 4 years old so it could be the car not allowing the battery to fully charge but overall it seems very similar to what MHT owners are experiencing. I would have thought the trickle charger would have brought the battery back up to 100% or close as it's just a standard 12v agm battery with no MHT complications involved.

[Beemer5to3]

Azure350z I use the NOCO Genius 5, and it took my battery from 48% to 81% (reading using Bimmercode). I suspect it would need to be connected for a good while to fully recondition the battery