What is the 12V battery load while car is off?

[GizmoEV]

What is the load on the 12V lead acid battery while the car is off? I only have a clamp meter which reads to the nearest tenth of an amp so I can only get an estimate. It looks like on my 2016 EV+ it is close to 0.5A. If this is true, that would mean that a 45Ah battery would be dead in 90 hours. This doesn't sound right, or the way it should be. I'm asking because this is what I was greeted with the other morning:

I wasn't sure what was going on at first but an attempt at power cycling the car showed me that the 12V battery was probably dead. It measured at 9.62V. Definitely a problem. I jump started with a LiFePO4 battery I have and went to work, ~15 minute drive. Torque Pro showed the Aux battery sitting at 13.7V both going to work and on the way home. When I've checked in the past, I usually see 14.2V. I parked the car and about an hour later I went to move it and the I didn't even get a reaction out of the car. I checked the voltage and it was at 6.36V while connected, and 10.09V after disconnecting the negative terminal. I put it on a smart charger for a couple of hours and then went to my local mechanic to do a quick load test. It tested fine. When I got home I disconnected the negative terminal and put it on the charger again and left it until morning. It still only showed 13.7V on Torque Pro. After sitting for a couple hours the battery voltage is at 12.7V, still connected to the car.

I believe the car was put in service in September 2015, I bought it in December 2016. I'm trying to figure out if the battery is just bad and I need to just replace it or if there is something else going on. AFIK, the car has had all of the software updates and recalls done.

 

[notfred]

There's a warning in the service manual that after the car is turned off various systems may still be powered on, I think it said something like up to 24 hours depending on configuration.

You can definitely tell that things are not a simple on/off switch - when you open the driver's door then the brakes pressurize. Similarly on turning it off the head unit clearly doesn't power down fully for a long time - if you return to the car after only a few minutes it is back up and running straight away, but if you leave it over night then it takes a while to boot up properly.

The LVDC converter can put out a lot of current, and unlike an alternator on an ICE it can give full power all the time. One of the early updates improved it running when the car was charging, but you say you have all the updates.

I'd check in Torque that the LVDC converter is actually putting out a decent current with the battery needing a charge and things like headlights and rear window heater on. Then I'd be tempted to just drop a new battery in, unless you have wired in anything then the odds are it's just the battery that died. There did seem to be a spate of them that died shortly after people bought the car a year or two ago.

 

[GizmoEV]

I'll probably have to replace the battery. This afternoon when I got home, the car was parked for a couple hours, then I moved it to wash it. After washing it, I moved it again. About two hours later I again moved it. A couple hours after that I hit the lock button on the key fob to lock the car and nothing happened. The battery was at 6V again. I decided to test what would happen if I plugged it in with the timer switch off. Nothing happened, not even a click. I got my LiFePO4 battery and hooked it up, still leaving the charge plug in. The LiFePO4 battery put out 31A into the 12V battery, settling down to 20A or so for the minute it was connected. Checking the current into the 12V battery from the DC-DC converter showed about 12A. Battery voltage was now at 14.2V. I lowered the EVSE current to 6A so charging would take a longer time and hopefully the 12V battery will be back to normal in the morning.

I have a feeling, however, that you are right @notfred. I'll probably have to replace the 12V battery. Maybe I'll hook my PowerLab8 up to the 12V battery and do a cycle test to see what its capacity is.

Someone suggested using an AGM battery. Any suggestions on a brand/type? I don't want to spend the money on a LiFePO4, especially given that there is a little time during the year where the battery will be below freezing and most Li-ion batteries shouldn't be charged at low temperatures.

 

[GizmoEV]

The 12V battery is definitely dead. I did a capacity check on it and came up with only 3Ah (45Ah originally) at the 20 hour rate! I think the only reason it lasted this long is because for the past year my wife has been driving it so it was getting one to two charges per day, depending on the day. This meant that the battery was getting frequently charged. This didn't leave much time for the battery to get depleted. For the past few weeks she has been driving the other EV so with my short commute this car wasn't getting charged but once/week. I'm also wondering if the 12V battery charges to ~14.2V during the entire time the car is charging. If so, then it is getting grossly over charged every time the car is charged, thus shortening its life significantly. Has anyone recorded the charging profile of the 12V battery during a full charge from a low SOC? If they aren't properly charging the 12V battery then they are murdering them.

I replaced the battery with an Odyssey Extreme 35-PC1400T. The battery is the same width, slightly taller, and a little longer. The only modification I had to do to the battery try was notch the molded hold down bar on the tray for two small support pieces in the battery case. It took me less than five minutes to make the modification with a Dremel tool. The only other modification I had to do was to the positive terminal post. Because the Kia post clamps have so much stuff around them and the Odyssey posts are recessed into the case, the positive terminal clamp mechanism didn't close enough. I used some scrap copper sheet and cut out a shim to wrap around the post, making it just big enough for the clamp to work. The Odyssey battery is about 20lbs heavier (45lbs rather than 25lbs) and has a 65Ah capacity. I went with the Odyssey AGM battery because I wanted a non-spillable design. I've had enough of battery acid corrosion in my prior EVs.