I bought a new 2019 Kia Forte last year, from the day I received it, its battery (lead-acid AGM) read a slightly low open voltage of around 12.45V. I figured out the car must have been driven on the dealer's lot for small distances therefore never got the chance to be fully charged.

Hooking it up to my own battery maintainer, I charged it as to around 12.7V which seems to be the norm for AGM batteries.

However, after driving a couple times for 100km+, I rechecked it and was dismayed to find the voltage near 12.3!

Over the course of the year, I found out that the battery likes to stay at 12.3, no matter what you do. It doesn't seem to fall lower, but without manual charging, it never gets higher.

According to my knowledge, 12.3 is not a good voltage level for a lead-acid battery to be at perpetually, it'll definitely lead to early battery failure. Right now I'm charging it every once in a while to keep to higher, but obviously this isn't a solution to the problem.

My nearest dealer is quite far, and they're probably simply gonna recommend changing the battery, which I know isn't going to work.

What could be the problem here? Electric leaks seems a bit unlikely since the battery level doesn't drop without stopping. Could it be the alternator is not performing correctly? If I were to take it to the dealer, how should I explain the situation to them?

Many thanks!

  • You are missing a critical piece of information. What is the temperature in which you measured the battery voltage?
    – juhist
    Dec 14, 2019 at 20:07
  • I take temperature into account. I use this tool to determine the state of charge: random-science-tools.com/electronics/lead-acid-battery.htm Dec 15, 2019 at 13:45
  • Oh, that's good. You should still specify the temperature that potential answerers know what the result was.
    – juhist
    Dec 15, 2019 at 14:09

1 Answer 1


The question is missing some important information (namely the temperature), but I'll still try to answer.

Modern cars may be micro-hybrids. This means that they purposefully leave the battery charge a bit lower than its maximum charge.

When decelerating (engine braking), the car computer decides to charge the battery at a high rate. When not engine braking, the car computer decides to charge the battery at a lower rate up to a partial state of charge. The reason for this is fuel savings. If the battery is predominantly charged when decelerating, it is using energy that would otherwise go to waste (heat in brakes).

Car batteries don't like semi-permanent partial state of charge. However, if you actually continuously use the car instead of just parking it, the battery will always sometimes be charged to full state of charge by the car charging system. It is just not all the time kept at this full state of charge.

I wouldn't worry. If the car is actually being continuously used, you will probably have a very good lifetime for the battery.

If such a car is parked for a long period of time, it is recommended to connect it to a battery maintenance charger.

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