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2017 Hyundai Ioniq Hybrid Limited with Premium Package
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This past weekend I went to a music festival and was camping for 4 days. My 2017 Hyundai Ioniq Hybrid limited was sitting for all 4 days and nothing was drawing any power that I’m aware of so my car was simply just sitting like it would at home in my driveway. Monday morning I pack my car up to head home and my car battery is completely dead so I hit the 12v reset button and it starts right up but because I wasn’t packed and ready to leave yet, I turned it back off but about 30 minutes later when I go to try to start it again the battery is dead again so once again I have to push the 12v battery reset button which starts it right up. I then drive home 8 hour drive and everything is fine but I took it to the Honda dealership today as a precaution to have them check everything out and they tell me everything is fine. This is my first hybrid and every car I’ve ever had had a 12 V battery under the hood that you just simply replace when it goes bad. But apparently the Hyundai Ioniq the 12 V battery is part of the main hybrid battery so I’m a bit concerned that once my warranty expires in about 30,000 miles (because I’m the 2nd owner it’s not covered by the lifetime warranty) then everything is gonna start breaking and I’ll be hit with an expensive repair bill. This is probably the 4th or 5th time I’ve had to push the 12v reset button by the way so i’m not really sure how that even works and how it’s aging my battery every time I push it. I admit it’s way simpler than trying to find somebody to jumpstart your car like a normal car but I guess my biggest question is how often do these batteries go bad and what do they cost to replace? Can the 12v battery even be replaced without replacing the whole hybrid battery pack? My car only has 48,000 miles on it.
 

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It is reasonably unlikely your 12 volt battery is failing, but it can and has been replaced separately - it is a separate item bolted on the side of the traction battery - no doubt that it would be costly out of warranty. You would have to use the OEM 12 volt battery - no one else would have one. Might be a chance of a less expensive source in Korea - I did get an OEM key fob direct from Korea for much less than dealer pricing.

However, either way, you have an issue with excessive current drain while car is off. I've had mine off for 5 weeks, did not need the "reset" button. I have used it twice, both times because of a (different) BlueTooth OBD reader I left plugged in overnight. Wet door latches (which are powered while car is "off") have been reported several times here - they get replaced under warranty as defective.
 

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Red 2019 Ioniq 38 Premium EV
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285 Posts
I have the 38 kWh BEV, now 22 months old, and yesterday I found the 12V just had died on me overnight! Was at 8.6V, enough to unlock the door, but couldn't start the car. And we don't have the battery-boost feature you have! My battery is the Delkor CMF40L-BCI, only 40 Ah and it's standard-construction, not AGM I believe. Nothing else around the same shape & terminals, so I'm going to get it checked out by dealer. Am expecting them to find nothing wrong!

So I'm now about to make my own battery booster device, this will be a 23 Ah Exide AGM motorbicycle battery, long but very slim, which will sit alongside existing. I'l arrange a beefy diode so it can be charged up from the car, but won't discharge back into the car, so won't go flat. Then if vampire drain happens, I'll press a small button which will operate a beefy Mosfet, like a massive relay in effect, which will couple-up the 2 battery +12V posts. This should give it enough boost to operate the high voltage contactors & start the car properly, then it wll be fine 'coz the big battery takes over he charging again.

I don't know if anyone's got to the bottom of these sudden battery-drains; is it the 12V's too small? Charged improperly & needs desulphating regularly? Door-switches shorting a bit thx to damp inside doors? Boot-light stays on if boot not 100% shut? Something else keeping the computer alive & draining it?

The only decent workaround I can see is having a beefy aux battery. I have a LiPo portable battery-booster for just this purpose, but that didn't have enough oomph!!! I suspect it couldn't cope wih trying to recharge a 12V sitting at 8.6V as well as pwoering-up the car, so now I'm doing a much larger version of this myself, in effect.
 

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I don't understand why the Lipo portable battery booster didn't work for you. This is what they are designed to do.
How do the specs of the motorcycle battery compare to the Lipo booster?
 

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Red 2019 Ioniq 38 Premium EV
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285 Posts
LiPo booster is an Ultrai, claims 22000 mAh, 81.4 Wh which gives me 3.7V. so equates to 6.7 Ah at 12V.
Exide is 23 Ah at 12V. So around 4x bigger.

Other data on label says:
Peak current 2000A
Starting current 1000A
DC Output 12-16V/10A (may be the Aux-socket connector)
I find it hard to believe it can output such a large cranking current, considering how slender the croc-clip wires are!
 

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Earlier this year I bought a Lipo battery booster: DBPOWER 1000A/12800mAh Portable Car Jump Starter
I have not had to use it yet. But I purposefully got one that was on the medium to low capacity since for my use it wont be required to crank over a gasoline engine. But if I do need to jump start someone else with an ICE it should be fine for that too.

So it confuses me that yours didnt work when all it should need to do is power up the controls. Maybe your portable Lipo booster was not fully charged?
 

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Red 2019 Ioniq 38 Premium EV
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It was charged up to 4 out of 5 LEDs on the scale, also it's got twice the capacity of the similar item Halfords sell, so it should have managed something. I wonder if the original battery at 8.6V was draining it substantially, and the rather thin looking cables couldn't supply that and also the car's computer stuff, so maybe these cables had a rather large voltage drop? I'm going to have to do some testing of this thing, connect it to a bank of 12V lights, or try starting my wife's ICE with it to see what it's really capable of.
 

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2019 PHEV Ultimate
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Monday morning I pack my car up to head home and my car battery is completely dead so I hit the 12v reset button and it starts right up but because I wasn’t packed and ready to leave yet, I turned it back off but about 30 minutes later when I go to try to start it again the battery is dead again so once again I have to push the 12v battery reset button which starts it right up.
The 12V Reset button doesn't charge the 12V battery, it just temporarily reconnects it.

Since lithium ion batteries are finicky to recharge safely with an external third party charger that knows nothing about a particular battery's design, there's a safety system that automatically disconnects the hybrid's 12V battery from everything in the car when it starts to get low (but before it gets too low to boot your car back up). The 12V Reset button just reconnects it for 10 seconds or so, allowing you to push start and get the car going. After that the car should be left going for at least an hour to charge the 12V battery back up. Too many resets without that recharging period and eventually the 12V battery would be dead dead, and require professional help to recharge or replace.
 
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