You can do it but not with a 'normal' battery charger you need a battery maintainer CTEK make the one I use for whichever car i'm not driving.

 

I have a CTEK... they are the best IMO especially for the price

 

Much of the debate over disconnect or not - or remove entirely - is historic based on old tech lead/acid batteries and ancient tech dumb chargers that had a tendency to boil the liquid and produce hydrogen. Then, a clumsy move when handling croc clips could spark and ignite that hydrogen. Back in the day, many mechanics lost eyebrows that way. So they recommended disconnection and /or removal to avoid that scare.

More recently the real danger is from sensors connected to the 12v DC battery that report to the computer mother ship and it isn't unknown for an eager charger to zap that sensor and cause problems if a charger is applied directly without disconnection.

For that reason I now disconnect the terminals on the battery and then connect the croc clips to the bare terminals. Many just disconnect the negative terminal and put the clip directly on the battery with the link to the car isolated. But some people still prefer to remove the battery completely from the car and charge in the garage for total safety from puter problems and for retaining eyebrows reasons. Not needed imo.

( These days it causes no issues with radio codes and the car just treats it as a re-boot session )

 

I've never disconnected the 12v in my E-Niro when charging the battery, it's been OK

 

Many thanks. That is good news. What charger do you use?

 

Providing you use an intelligent pulse charger there should be no issues. Also lock the car once you've opened the bonnet and putting your key into a pouch or back in the house, to prevent your car from waking-up during the trickle charge.

 

Sorry,but why do you need to charge the 12V battery, I thought that was all taken care of by the car itself

 

It should not be necessary - but it is. Most problems happen because drivers ignore the 12v battery and are not aware that some situations allow it to become low in charge. So that unknown to the driver a spiral is beginning. That low charge is often just about sufficient to start and run the car, but if the same driving conditions continue then by starting at that low charge it later becomes even lower and eventually fails - often at an inconvenient place and time.

They then jump-start the car and it is a case of 'rince and repeat' until the next failure, at which time the battery will have become so damaged that it must be replaced. This pattern has been seen for years as the OEMs fail to install adequate algorithms to run the onboard DC to DC converter to cover all use cases. We know this from bitter experience and years of complaining.

Eventually they will solve this festering issue and some progress has already been made but until then I have been taking measures to both keep a close eye on the 12v DC condition and to keep it in good condition overall by using a smart conditioner mains charger once a month whether it seems to need it or not. They first of all analyse the condition and then instigate a repair programme if something is out of spec. Then go on to use a planned programme for that condition and in some cases run a desulphide session. The charge itself continues until all cells are balanced. Your Dad's old and rusty dumb charger doesn't do this.

I do this as part of the monthly tyre kicking and screenwash bottle filling routine as preventative maintenance and over the last seven years in three EVs I have escaped the often reported 12v issues. As you say, it should not be necessary but life is too short to be stressed by such things. I now know that the 12v DC battery is in good condition by observing the BM2 monitor and the plugin voltage gizmo in the cabin. If people choose to ignore the 12v battery condition day to day, and are oblivious to whether it is OK or gradually reaching a low stage of charge then that is for them to decide. Almost all people do that of course, and most get away with it. Until they don't - and then they start another thread in here to complain about it.

 

I have a RING Powering Smart Charger, and usually hook the car up every couple of months, It's no real hassle and if it avoids low 12V problems then why not. I also used to do this with my previous ICE car.

 

I've got a noco genius 5 that I've used a few times on my niro PHEV battery with no issues.

 

Given I cannot even open the bonnet of my car……and the advice in the manual re charging the 12v if it is needed is to take it to a service centre……..Mercedes Me app does show the state of the 12v and I have seen it partially charged but revert to fully charged without the car having been started so hopefully Mercedes have now designed the system to look after the 12v. The EQC only threw up the frightening array of brain dead error messages once but a turn off close lock and reopen was enough to sort things out the 12 v having probably just got enough charge the time I was looking and wondering what the hell was happening.
The EQE SUV was plagued by brain dead error messages of various sorts on early deliveries all reminiscent of a 12v battery issue and a software upgrade is the most talked about solution which has apparently addressed it and given my experience it seems it might have🤞

 

I've posted on a different thread about the charging of battery when not in use. The Kona BMS software charges the battery every 4 hours when locked/ not in use. Kia will be the same I'm sure. So no trickle charging required. My battery is pretty much at 100% charged most of the time. Even when parked up at airport carpark for a week in the freezing cold.
If you feel the need to charge, leave the battery connected but the negative connector on the charger needs to go to body earth point and not negative terminal. Putting on the negative terminal will bypass the 12v battery monitoring sensor which isn't recommended.