[79Bry]

My 2023 Ioniq5 EV 12 V battery died at 26,000KM and 27 months with the main battery showing 74% Warranty is 12 months. I had to use a portable charger to get the voltage to 12.6 volts but it failed again the next day. Dealer wanted $530 Can. to replace and diagnose. I purchased the equivalent from Costco with a 4 year warranty and installed it myself. It has been holding up but it always shows around 12.45 V when I open the hood and check it. This is considered a low charge according to every battery manufacture and leads to plate sulfation and a shorter than normal battery life. I was in twice for the ICCU converter software recall. I don't find this acceptable on Hyundai's part as the charging issue still appears to be present and the consumer pays the price.

It's been reported that when the hood is open the battery is under additional load, so it'll be normal for the battery voltage to read lower. This is one of the reasons people get a remote battery monitor, it can be installed on the battery to record voltage with the hood being closed.

 

[GregBrew]

My 2023 Ioniq5 EV 12 V battery died at 26,000KM and 27 months with the main battery showing 74% Warranty is 12 months. I had to use a portable charger to get the voltage to 12.6 volts but it failed again the next day. Dealer wanted $530 Can. to replace and diagnose. I purchased the equivalent from Costco with a 4 year warranty and installed it myself. It has been holding up but it always shows around 12.45 V when I open the hood and check it. This is considered a low charge according to every battery manufacture and leads to plate sulfation and a shorter than normal battery life. I was in twice for the ICCU converter software recall. I don't find this acceptable on Hyundai's part as the charging issue still appears to be present and the consumer pays the price.

When you open the hood, the vehicle "wakes up", and there's a load on the 12V, which might be dragging it down a bit. Also, during the time that the hood is open, the vehicle does not monitor and charge the 12V auxiliary battery.

I highly recommend installing a BM2 battery monitor, on the 12V auxiliary battery. You can get all kinds of useful info about 12V battery health and vehicle charging, and the Ioniq is not awakened. The BM2 is relatively cheap (<$25), and an easy DIY install.

Edit: Hah! Looks like 79Bry beat me to it, by seconds.

 

[rds1718]

I am new to the Ioniq 5 family (2025 RWD Limited) and have read some of the ICCU info but I'm still not clear of the following.
1. Is there any correlation to the OEM battery putting extra strain on the ICCU?
2. If I were to swap out to an AGM while the car is still new is that in any way making an ICCU failure less likely?
3. Has anyone created a poll that has 12V battery type and ICCU failure yes/no?

 

[JerryP]

You can learn a lot about people's experiences in the ICCU thread if you haven't alreay perused it.

1. Is there any correlation to the OEM battery putting extra strain on the ICCU?

No statistical evidence, but it seems likely since the AGM initiates less frequent charging sessions.

2. If I were to swap out to an AGM while the car is still new is that in any way making an ICCU failure less likely?

I'm hoping so.

3. Has anyone created a poll that has 12V battery type and ICCU failure yes/no?

I don't think so. I have seen one or two reports of people with AGM batteries having ICCU failures, but they had had the OEM one quite a while before making the change, so maybe the damage was already done.

 

[Neil F]

1. Is there any correlation to the OEM battery putting extra strain on the ICCU?

Some have theorized however there is no factual information. My point is while Hyundai has not done anything, if it were as simple as changing the battery I believe Hyundai would have done this

2. If I were to swap out to an AGM while the car is still new is that in any way making an ICCU failure less likely?

Per the above there is no factual correlation between the 12v and ICCU failure

3. Has anyone created a poll that has 12V battery type and ICCU failure yes/no?

……dozens and dozens many I5, 6 forums

 

[battman]

Any owners using a Sodium battery yet ? reports ?

 

[R P]

While I am not aware of any true statistically valid info, I have seen enough anecdotal posts on this forum to lead me to believe that indeed too frequent yellow light charges can stress the ICCU and lead to failure. In my case, before the ICCU failed, the yellow light would come on constantly. And when the ICCU did fail, the 12V was also toast and had to be replaced. And I have seen many similar situations here from posters.

My dealer could only replace the 12V with the same OEM flooded battery. But I replaced it with an AGM on my own, and the OEM is currently sitting in my garage. The service advisor did agree, however, that an AGM would probably be better.

I do know that flooded batteries can be damaged by being completely discharged. This is old news. But I believe they can also be damaged by constantly being charged at too high a rate, esp when they are near full. From by BM2 I see that the charge rate is normally at 14.8V. That is too high unless it is doing an equalization session at low current. But that should happen only once a month for flooded batteries, not with every charge.

I have an off-grid solar system at our cabin, which includes 16 6V batteries. It has a charge controller that has several charge phases to properly charge the batteries and protect them from overcharge. When the batteries are low (say 60%) the first phase (Bulk Charge) starts at a high charge current and 14.6v (12v equivalent). Then as the SOC gets higher the current (not the voltage) decreases. When the batteries reach 100%, the current drops to very low current, and the charging voltage stays constant at 13.5V similar to a trickle charger in your garage. Once a month it automatically does an equalization charge at 14.8v and very low current for one hour to balance all the cells. Some of my batteries in my system are 10 years old and still going strong.

What we don't know with our BM2s is how the current changes with SOC. We do know with fast DC charging the current really drops after 80%. Whether the same happens with the 12V charging would be interesting to know.

I should mention too, that my other EV (Solterra) also has a BM2 and I never see a high SOC charge, usually only about 14.2V which is actually pretty low, but OK to top off a battery when needed. The flooded OEM will be 3 years old in Jan/26 and so far seems to be doing OK.

And an AGM can not only withstand discharges better, but also can be charged at a higher SOC. So that is why I believe it is a better battery for our cars.

 

[rds1718]

I had bought a BM200 but never installed it so I did just now. As soon as I did I saw the SOC was at 47% and dropping. The voltage started at 12.3 but quickly dropped to 11.9. I plugged the car in and everything started going up. Should I be concerned with this? 2025 I5 Ltd.

 

[Daedalus]

From by BM2 I see that the charge rate is normally at 14.8V. That is too high unless it is doing an equalization session at low current. But that should happen only once a month for flooded batteries, not with every charge.

I mentioned this too in another thread. The charge controller is cooking the battery. Last week I put in an AGM battery. The factory battery I removed had been replaced under warranty just over a year ago, prior to my purchasing the car. My battery tester showed it to already be in a poor state of health, with barely 400 cold cranking amps in it, vs. the 650 it should have. Notably, my ICCU failed 5 months ago, though it was still charging the 12V battery.

These are the recharge profiles. The AGM is probably recharging more frequently because I also changed my dashcam settings for always-on sentry mode at the same time (thought I had already made that setting when I installed it).

 

[Mikael48]

I mentioned this too in another thread. The charge controller is cooking the battery. Last week I put in an AGM battery. The factory battery I removed had been replaced under warranty just over a year ago, prior to my purchasing the car. My battery tester showed it to already be in a poor state of health, with barely 400 cold cranking amps in it, vs. the 650 it should have. Notably, my ICCU failed 5 months ago, though it was still charging the 12V battery.

These are the recharge profiles. The AGM is probably recharging more frequently because I also changed my dashcam settings for always-on sentry mode at the same time (thought I had already made that setting when I installed it).

View attachment 62462

Does this graph show just 1 day (20 hours), no driving? If so, you put a great strain on the 12v battery with the dashcam.

There seem to be some additional drain every 20-30 minutes, maybe Home Assistant integration, or utility company using your Bluelink?

 

[MIkeS]

While I am not aware of any true statistically valid info, I have seen enough anecdotal posts on this forum to lead me to believe that indeed too frequent yellow light charges can stress the ICCU and lead to failure. In my case, before the ICCU failed, the yellow light would come on constantly. And when the ICCU did fail, the 12V was also toast and had to be replaced. And I have seen many similar situations here from posters.

I think this may be cause and effect getting mixed up. If the ICCU is failing the 12v will not be maintained correctly so the yellow light would be on more often. When the 12v gets drained it will no longer take a full charge and need to be replaced.