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tillathenun's picture
12v battery died (on Kia e-Niro)

Sorry if this has been discussed before but I had my 12v battery die while OVMS was plugged-in.

I've not had OVMS plugged-in for ages (not much need during lockdown!) but we've just gone away for a week and it happened then after only one full day of inactivity.

This has happened before and the common theme then and now is that the car was seemingly left unlocked.

The e-Niro's battery saver module is supposed to kick in of course but I don't see how the voltage could drop so much in one day anyway. I do have the ABRP script installed now so I imagine that could make a difference?

You can see from the screenshots attached that my notifications show what happened.

  • August 19th: Drops 1.8V in only 32 minutes. e-Niro's battery saver then kicks in and restores it.
  • August 20th (car was unlocked): I woke up to all the notifications where it dropped as low as 4.8v. Battery saver obviously did nothing as when I got to the car it was dead.

So, my question is:

Does the module not 'sleep' properly if the car is unlocked? Could that be why the battery was drained so quickly? Is there any way to get around that?

I'm making a video about it so I'd like to get my facts straight first before I jump to conclusions!

August 19th part 1 August 19th part 2​ August 20th

inf0mike's picture
12v battery issues

I recognise your username (I watch your channel) and I feel bad because I was the person who tweeted you about ABRP script a few weeks ago! 

I have a Kona and have also experienced a dead 12v battery for the first time this week.  I have left the OVMS on and the abrp script active for weeks without any issue and initially I suspected that the recent BMS update was to blame. After the BMS update the Aux battery saver option disappeared from the car menus and from the number of notifications from OVMS, it seemed to be topping up the 12v battery two or three times a day.  Then, all of a sudden I seemed to give up doing aux battery saver and then within 24 hours the 12v was dead.

The OVMS module draws some power itself but also, in order to give you status of the car I believe it causes some of the cars ECUs to remain awake which then further increases battery drain.

I think there is an issue with the Kia / Hyundai 12v battery systems because many people have reported problems and none of them were using OVMS.  The open vehicles documentation does declare that it can drain the battery and I think that OVMS tips the already delicate 12v system in our cars just over the edge.

For me, I think the solution is to get into the habit of turning off OVMS when I am not using the car.

Here is my switch solution:

Best regards,

Mike Stuart.


inf0mike's picture
12v battery issues

I would also like to point out the irony that my 12v battery died while the car was in my own garage and plugged in with 70% in the main battery.  There is certainly serious argument that the vehicles themselves are not managing the 12v system properly.

See this thread on speak ev Kona forums: https://www.speakev.com/threads/flat-12v-battery-even-with-aux-battery-saver.140408/.  People buy and keep 12v booster batteries in their cars now: https://www.speakev.com/threads/12volt-battery.152319/


Mike Stuart.

markwj's picture
> Does the module not 'sleep'

> Does the module not 'sleep' properly if the car is unlocked? Could that be why the battery was drained so quickly?

The OVMS module is continuously powered by the car, even when the car is off. While the OVMS module uses extremely low power, it does continuously draw power from the car’s battery, so it will contribute to ‘vampire’ power drains. The implementation is very much dependent on the actual car type, but most electric cars have a small 12V battery which could get depleted if OVMS is left active for long periods (weeks) without charging. 12V battery usually is charged concurrently with the larger main battery or when the drive train is enabled and the Auxiliary Power Module provides electricity from the main battery to 12V peripherals.

> Is there any way to get around that?

If power saving features are enabled, some modules can be switched off after certain time period of inactivity (non charging). The power management module in OVMS monitors the 12v battery level, 12v charging (if your vehicle implementation in OVMS supports that metric), and on/off state of the car. It will shutdown higher-power things such as the modem and wifi, when the car is sleeping. You can find the configuration for this in the web interface under Config / Power Management. The modem is by far the biggest power usage in OVMS, followed by Wifi. With both turned off, OVMS consumes very little.

Regards, Mark

same issue with a 2017 Soul EV

I have been experienceing the same issue in my 2017 Soul EV (Luxury).
OVMS has been installed since the summer.  The 12V battery is new installed in December.

With the pandemic, my wife and I are both working from home and now our only use of the car are the short 10 minute trips to drop our son at school.

Before the winter deep freeze, we would only have to plug in by the weekend.  But overnight, we have been "blessed" with -17C weather.  I woke up to multiple battery low warnings and a fully dead car.  I had to use the key to open the dirver door, reach to the back door to manually unlock it and then fold dow nthe back seat to rummage in the trunk for jumper cables.

The car was set to start charging at 04h, and then to pre-heat the cabin at 07h20 (07h50 departure).

The OVMS 12V battery history shows that starting around 02h40 there's a little "jitter" in the battery voltage that seems oscilate between 11.9V and a diminishing low, until voltage drops off a cliff.  To me, it looks like voltage is more or less steady, then a load kicks in and voltage drops, the load stops ad voltage recovers somewhat.  This happens in groups of 6, about every 10 minutes for an hour, at which point the "recovered" voltage is under 8v.  Then, at 04h, the charger is supposed to kick in but  by that time, the 12v battery has fallen to 4v.


So at 07h this morning, I put a 4S 100ah LFP pack in parallel with the 12v battery and measured current flow with a clamp-meter.  35A was flowing into the 12V battery.

The car started fine and was bale to charge and heat the cabin.  I left the car idling like that, while plugged into the L2 charger and disconnected my LFP battery. Current into the 12V battery was about 9A, I am assuming from the onboard 12V charging circuit...


We got home by 08h15 and plugged back in.  Charging timer still set for 04h, and the second pre-heat timer is set for school pickup.  AS I type this, OVMS just pinged me about voltage dipping to 11.0V.  So. I will go turn on the car again...

My current theory is that with such short trips, the car never gets to properly recharge the 12V battery ans so it is gradually brought down to the point where now, it is so undercharged that the vampire loads are neough to drain it.  Add in some col weather and we get this stiuation I now find myself in.


Any other theories?  Any way to do an energy audit of the various circuits, or perhaps sniff some CANbus traffic?

I also see some oddness with the Charger Temp (*C) line in the 12v battery history graph.  The temperature sometimes seems to rise with no explanaiton...



forester's picture
some issue,on a 2020 Kia e-Niro 64 Kw

My battery ( 2020 Kia e-Niro 64Kw with 2500 Km. ) also discharged the night after a 20-minute drive on the highway, I called the roadside assistance service, who started it with an emergency starter (mine was In the trunk, which I could not open with the battery discharged and without being able to deactivate the parking brake) When I took the car to the workshop to have the damaged battery replaced, they told me that the battery was fine, once recharged.

Once a lead-acid battery has

Once a lead-acid battery has dipped low - it's best to replace. A typical lead-acid battery will experience sulfation pretty quickly. If the garage stated "your battery is fine" - that's because they tested open clamp voltage. Under load - it will quickly sag. Keep an eye on it..

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