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Discussion Starter · #1 ·
I'm not using my 2020 Kia Niro that much but enough and I keep the main battery usually at 80% charge.

Seems to me that in any case, the small 12 volt battery should be always well charged by the main car battery, right?

It happened already 3 times that the 12 volt battery went empty and I couldn't start the car. Our Kia dealership people came up with all kind of reasons for that that didn't make any sense to me. The way my logic goes is that as long as there is power in the main battery, the small 12 volter should always be charged and ready to go. dc to

Am I wrong thinking that or do I have a bad DC to DC converter?
 

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2022 Bolt EUV Premier
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2,937 Posts
Unfortunately, no. The DC-DC converter is generally only in use while the car is "running". I would expect it to monitor the 12v voltage level, as the PHEV does, and activate the battery saver mode. But if there's some sort of phantom power drain (like a light left on), even the battery saver will only trigger a certain number of times. After that, it lets the 12v continue to drain. The real problem is the lead acid batteries used in the PHEV and EV are not deep cycle batteries, which they really should be because of the way the car charges them. A car with an engine usually has a generator/alternator that is continually charging the 12v battery, which is what a lead acid battery wants. In PHEVs and EVs, they use the DC-DC converter and charge the 12v from the main traction battery. However, this is not continuous like the alternator, so the battery goes through peaks and valleys of charge level, which isn't good for them long term. It's likely all in the name of cost cutting. The smart thing would be to use a battery tender to keep the 12v topped off when the car is parked for an extended period of time.
 

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2022 Niro PHEV Ex Premium
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I learned a lot about those 12V batteries and how to maintain them in this thread.

(Just be sure to note that there are some 12V battery differences between EV, PHEV and HEV models, and also perhaps battery types by year or region. Check what you have.)
 

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Kia E Niro 2019
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8 Posts
I think it is useful to have a “palumma voltage meter cigarette” (to find on Amazon) always in your cigarette lighter outlet. When you turn on accessories it will give you the voltage in the twelve volt battery, currently for our 2019 Niro EV = 12.6 to 11.8. When my car is On the meter reads 14.6 to 14.8. When I am charging with my level two charger and I turn on accessory it shows 13.1 volts. So either On or charging the twelve volt is being charged. It seems to me that a deep cycle battery would be more suitable. I have been paying attention to the twelve volt battery recently thinking it might need to be replaced, but not sure how to tell. Does it sound weak when starting (nope never does starting).
 
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