Auxiliary Battery Charging - an Observation

[Tim94549]

A couple months ago I experienced the Dead 12v Battery issue; unexplainably. I read a lot about how the Battery Saver works - requiring a minimal 40% SOC of the traction battery - it then periodically tops off the 12v Aux Battery. (I had previously allowed by traction battery to get down to around 20% before charging).

So at various times overnight, I get the Bluelink alerts about my doors being unlocked - which they are since it's securely parked in our garage. I get these alerts around 4 times per night (or day - when parked for a long time). The alert times seem to be every 4 hours. My thought/belief is that THESE are the times that the Aux Battery is getting topped. And if true, I believe that if I allow the SOC to get below some threshold (40% ? 35% ? 30% ?) that I will no longer receive those alerts and thus the Aux charging will no longer function.

Thoughts about this ? Am I on to something ? MY 2020 Ultimate

 

[KiwiME]

If you had a BMS update in the last 2 years you might find that number is now 50%. But it always charges the 12V battery once a day anyway.

I think installing a BM2 on the 12V battery might offer useful information.

 

[Tim94549]

I haven't had any BMS update for several years. But 50% ? that's crazy that we're required to maintain a SOC of 50% just to keep the AUX battery from going dead. This whole AUX battery thing isn't designed very well, imho .. I mean, what happens if we're on a long trip and the traction battery gets down to 15-20% ... this all implies to me that there is no AUX charging at all until we get the Traction Battery topped up.

I have a battery tester that I just leave plugged into the 12v thing in the console. So I keep an eye on it that way. And so far (since my battery drained a couple months ago) it's maintaining 11.8 - 12.4v .. I was just thinking that what I was seeing via Bluelink (doors open) was that the car was waking up to top the AUX battery and found the doors unlocked at the same time .... It's pretty consistent - every 4 hours.

 

[KiwiME]

Consider that the 1st-gen Kia eNiro (2018-2022) has always only charged the 12V battery once a day, just like the Kona did originally when it had the "Aux Battery Saver" dash option and that was unchecked. Kia seems to occasionally disagree with Hyundai. The Kia forums are no more full of battery complaints than the Kona forums. But both certainly have many.

By further evidence the Kona can only detect a low 12V battery at the moment it wakes up to carry out a charge. When that happens it reacts by adding a further charge event 1-2 hours later instead of waiting another 4 hours.

But whether the window of opportunity to fatally deplete it is 4 hours or 24 hours, either is plenty of time. And what threatens depletion more than anything in my years of BM2 observations is simply turning the car 'off'. The traction battery is taken off-line the moment the button is pressed and so cannot support the shutdown process.

Every "off" event leaves the 12V battery slightly depleted as it needs 9 minutes to fully reduce the 12V current draw to the standby level. While parked, the battery will be fully charged again only at the next scheduled charge event.

What can catch drivers out is when they drive multiple shorts trips in a row, especially where they may have the doors open for longer than it takes to get out, such as while doing deliveries. Short trips don't offer much productive 12V charging time while driving and it adds up.

Unfortunately Hyundai-Kia has apparently decided that this methodology was good enough and furthermore it was too complicated to explain to their customers what simple precautions they could take to minimise the risk of a problem. They could have left the traction battery online for 20 minutes after every stop which I suspect would have significantly reduced complaints.

My best and final advice to yourself is to drop off that cigarette-lighter voltmeter at the nearest charity shop and buy yourself a BM2 voltage logger. Replace your 12V battery because the voltages you describe (if accurate) are below what they should be. An AGM battery type is a good option and be sure to let 12V power lapse during the changeover so that the car knows to reassess what it finds.

Subsequent to swapping batteries, let the car sit locked and undisturbed for 3-4 hours if that's practical, which is per Hyundai's service docs. In my experience doing this, I needed to charge the traction battery for a short time first (10-30 min) to kicks off that process, but remove the charge plug when that's done.