Put the car in Utility Mode for a number of hours. This will give the 12v a good charge. But it's a 5 year old car. Keep an eye on it.

 

Does this mean my 12v battery is on it's way out?

Could mean that the 12v is low, not necessarily buggered.
Possibly if you have been “playing” with the new car whilst a novelty to you. Doors/Boot open etc and setting up preferences whilst in auxiliary mode ( ie just the ignition “on”)
Do what @Xinix advises👍

 

Possibly if you have been “playing” with the new car whilst a novelty to you. Doors/Boot open etc and setting up preferences whilst in auxiliary mode ( ie just the ignition “on”)

Never put the car in auxiliary mode!
At least, not for any length of time over a few seconds.
Yes, utility mode for charging the 12V battery and also for any messing around with the car switched on e.g. I use it when using the tyre inflator.
In utility more everything is powered from the traction battery and the 12V gets charged continuously.

 

Had battery checked and it is a good battery but only charged to 76%.
Sorry for being a noob(our first EV) but how do i put it in "Utility mode"?

 

Ok. I have put car in utility mode and left it locked on drive. Is this now charging battery?
What do i do after leaving it a few hours on Utility mode.
Do I go to car and turn Utility mode off?
Thanks

 

Ok. I have put car in utility mode and left it locked on drive. Is this now charging battery?

Yes, exactly as though you were driving.

What do i do after leaving it a few hours on Utility mode.
Do I go to car and turn Utility mode off?

Yes, unless you need the car to provide power to lights or to accessories such as the sound system.

 

Tried multimeter on 12v battery and it only charges if I leave car ready to drive away with keys inside. obviousley I can't leave car on drive with keys in.

 

Tried multimeter on 12v battery and it only charges if I leave car ready to drive away with keys inside. obviously I can't leave car on drive with keys in.

I seem to remember it's not very easy to leave the car unattended in utility mode. I think you have to do something weird like lock the door with the mechanical key from inside the key fob and ignore the warning squeal that the car makes for a few seconds.

 

IIRC, utility mode in fact charges the car at a higher voltage than at normal driving in the Niro. But if yours isn't doing anything unless you are in "ready to drive" mode, that's very weird.

 

Would I be better off just charging the 12v battery with a charger?
The manual says to take it off the car.

 

If you have one, use it if it's simpler.
Several others on this forum have reported no problems with charging the 12V while in the car and connected, but it's obviously at your own risk. I have disconnected my 12V battery temporarily for other reasons, and can confirm that the car doesn't mind a bit having the battery removed for a while and reconnected later.

 

An hour in Utility Mode should be plenty sufficient to completely sort out any residual charge issue if indeed the 12V battery itself is not knackered.
Put the car in Utility Mode, sit in it with the keys, and read a book or play games on your phone for an hour. I wouldn't bother with removing the battery etc, as that's a hassle you can easily avoid.

 

A 5-year-old battery could be on borrowed time, if you see the error again think about replacing the 12v battery. I had the same error in my classic Ioniq but ignored it and paid the price with a flat battery and being locked out. I gave the battery a charge, but it failed again so I replaced the ailing battery and all was well again.

 

I've put car in utility mode and left on drive with keys in. Showing 14.5 v.
Put Disclok on to keep it safe.
Will let you know how I get on. If it doesn't work will get a new battery.
Thanks every one in the meantime

 

I use a Ctek MXS 5.0 charger. Great bit of kit, you can do a Desulphation repair-cycle with it. takes about 24 hours to do. If leaving the battery in the car, probably a good idea to disconnect the Earth terminal so the car doesn't do one of it's 6-hourly periodic topups at the same time as Ctek's also playing around! I managed to keep a damaged 12V battery in my Ioniq 38 going for quite a while like this. But since I fitted a Yuasa the car's been doing far fewer periodic topups.

Original Delco battery is not an AGM, just an "ordinary" lead-acid when you select the options on the Ctek. But we have suspicions that the car was originally designed to use an AGM, H just cheaped-out when they built them.

 

After car had been in utility mode with "ignition" on for half an hour, it sent a warning to app saying leaving it in this state I.E. on and not running, could cause damage!
So i turned car of and the battery was now up from 12.1 volt to 12.4 volt, so it had already put some charge in it in that 30 min.
I will check battery again tomorrow to see if it is holding its charge.
If not I will replace the battery.
Any recommendations?

And thanks for everyone's help.
This is a great forum.

 

So i turned car of and the battery was now up from 12.1 volt to 12.4 volt, so it had already put some charge in it in that 30 min.

It's good that it's charging, but still quite low and not fully charged which should be 12.6 to 12.8V.
See 12-Volt Lead Acid Battery Voltages: A Comprehensive Guide To Capacity And Performance [Updated On- 2025] for example.

 

That warning is rubbish. You can safely leave the car in Utiliy Mode for a couple of hours. It is the same as Ready mode with the difference that Drive cannot be enganged. But the HV battery is active and so is the DC-DC converter for the 12V circuit. If this can damage the car, then so could driving the car.

 

why can't drive be engaged? my car wont go into utility mode without me pressing the stop/start button and the brake pedal at the same time!
So it is ready to be driven surely.

 

Usually, you go into Utility Mode after having started the car in Ready Mode.
But you cannot exit Utility Mode back to Ready Mode (and hence then drive). You can only turn the car off to exit Utility Mode.

 

Another vote for the Ctek chargers, in my case I use a 0.8amp job. It will automatically electronically clean a sulphated battery and bring old batteries back to as good as new unless it has warped plates.

 

As mentioned before, get yourself a Smart charger, various brands available and one of these below.
£100 on Amazon and keep it in the glove box, not in the boot.
Welcome to the wonderful world of EV vehicles. 👍

 

Will I have to disconnect battery to charge it?

 

I always do.
Just as an example, I replaced the original failing 12v battery 3 years ago with a Yuasa replacement. The car has been fine with the new battery with no battery warnings, that is until yesterday. So, today I’m charging the original (failed) battery and will temporarily replace the Yuasa with it. I’ll then charge the Yuasa battery using the CTEK chargers recondition function, it’ll probably take all day. I’ll swap the batteries over when the Yuasa is fully charged again and hopefully de-sulphated.

If I get another low battery warning, for peace of mind I’ll replace the Yuasa battery with a new one. I know what its like being stuck on a cold rainy night with a flat battery, with no shops open and a 4-hour recovery, it’s not pleasant…

 

You should do so because otherwise there is the risk that the HV battery will charge the 12V battery simultaneously.
As the timing of when the car decides to charge the 12V battery is somewhat random within the limits of either time since last done or voltage drop in the 12V battery, you cannot know precisely when it will happen.
Much safer to disconnect the 12V battery from the car to stop anything else from happening.

 

That Noco model is a boost emergency-start device, not a battery charger. Advice to keep it in the car for emergencies is good.

With a trickle charger connected, you (probably) don't need to disconnect the battery from the car. Every now and again the car checks the 12V voltage and will switch on its DC-DC converter for a boost if it thinks it needs one, but if the battery's already under steady charging it wil just discover that more's not needed and go to sleep again.

I firmly suggest, though, never to use desulphation (sometimes labelled repair or pulse) charge mode unless the battery is disconnected from the car. That pulses a quite high voltage into the battery and, if you're unlucky, could cause very expensive electronics damage to the car; even if not damaged, the car's many little computers might go temporarily insane from their unstable pulsing power and need fault codes resetting. Normally just disconnect the negative terminal and clip the charger to the bare battery post.

Just checked my spreadsheet of battery voltages... the significant difference (for a car) between a standard and an AGM battery is that the Uo (initial, fast boost) charging voltage can be up to 15.0 volts for a standard battery at 20C but only 14.4 volts for AGM. If you fit an AGM to a non-AGM car there's a possibility the battery's working life will be shortened by over-charging, and if the other way about, the battery's life might be shortened by charging too slowly.

My suggestion for most EVs is that at the first sign of a 12V battery getting tired, if it's out of guarantee and over 3 years old, replace the battery. If that's a DIY replacement for £100 every 5 years, the cost per year is probably less than running the battery for longer until you have a car that won't start, in the least convenient place and at the least convenient time.

 

That Noco model is a boost emergency-start device, not a battery charger. Advice to keep it in the car for emergencies is good.

I never said it was a battery charger!
I also advised him in my post to get a Smart charger. Personally I use a RING model.
I’m sure the OP knows the difference between the two.

 

Because battery is 5 years old I think I'm going to bite the bullet and fit a Yuasa HSB012 with 5 year guarantee.
My son has got a trade card at Halfords so should get it for about 70 quid.
I know from experience Halfords are decent at honouring their warranties.
As an aside, when I preheat my cabin,I assume it takes the energy from the main battery not the 12v one? Is this correct?

Thanks everyone for your help.

 

As an aside, when I preheat my cabin,I assume it takes the energy from the main battery not the 12v one? Is this correct?

Yes.

The 12V power circuits run just the lights, fans, contactors, actuators, small motors, all the computers and sensors and anything you plug into the 12V power socket(s). Heating, aircon and the hefty electronics and motor(s) to drive the wheels are all run from the traction battery.

Because battery is 5 years old I think I'm going to bite the bullet and fit a Yuasa HSB012 with 5 year guarantee.
My son has got a trade card at Halfords so should get it for about 70 quid.

Any quality 012 battery with adequate capacity (Ah, ampere-hours; ignore the advertised CCA for a battery as irrelevant to an EV) will work. Yuasa is an excellent brand. Bosch, Varta and Exide are also good. Others may well be. That's a decent price, or outstanding if it includes installation.

 

Do check the terminal post sizes of the various batteries. My '38 takes UK sized posts. and some Yuasa are the smaller Japanese, so need shims to fit. I always use tayna.co.uk for my batteries, and they also have all the terminal post info in there.

 

I have used Tayna for replacement batteries for friends and family for a few years now. Their prices are competitive, and delivery is usually the next day. I queried the post sizes when I ordered the battery for my Ioniq, when the battery arrived the correct post shims were fitted to the battery.