12V Battery condition?

[travellerva]

I had a long trip away from home and left my 2014 Model S 85 hooked up to my charger for 10 weeks while away. I set the charging capacity to 50% to keep the main battery healthy. I also hooked up a battery conditioner to the 12V battery to avoid it being drained.

On my return yesterday, the battery conditioner on the 12V battery showed it to be in good condition - all green lights. However, when I started the car I had the "Replace 12V battery soon" message on the dash (the battery conditioner had been disconnected prior to car start). The message remains on the screen after a short (3 miles) trip and is still showing.

Has anyone had a similar situation? I'm sure if I take the car to the SC, they'll just replace the 12V battery but why would this be necessary if the battery conditioner shows it to be in good shape? The battery conditioner is a top quality conditioner and quite new.

 

[kermit_xc]

what's the reasoning behind the 12v "conditioner" ?

 

[Lasttoy]

Even if it's bad u can replace it at half the cost of SC.
But all u had to do was leave car plugged it like u were home.

 

[Tam]

what's the reasoning behind the 12v "conditioner" ?

There's a long thread about using a separate charger to keep your 12V charged to take the burden of that job away from the main battery especially when owners are on vacation and thus to avoid excessive vampire loss.

 

[Tam]

..."Replace 12V battery soon" message...

Would a reboot help the clear the error message?

What's your 12V battery measurement. Mine is 13.8V.

 

[ewoodrick]

I know that there's a lot of discussion on the S/X and the 12 V battery, but here's my take.

The car knows hot to charge the battery. It can probably do a good job as long as it is within normal parameters. If you have extra devices attached to the 12 V, it will probably have negative effects.

For @Tam, if your 12V Lead Acid battery is showing 13.8 V at idle, there's an issue. A 12 V batter should ONLY show 13.8 when under charge. The second that you remove the charge, it at drop back under 13V, closer to 12V, hence the name of 12V battery.

 

[kermit_xc]

There's a long thread about using a separate charger to keep your 12V charged to take the burden of that job away from the main battery especially when owners are on vacation and thus to avoid excessive vampire loss.

Long thread in the internet ... oyyy

 

[Silicon Desert]

But all u had to do was leave car plugged it like u were home.

Yes, I never try to over think this as well. I just plug in the charger and that's it. Been gone weeks at a time on several occasions without issue.

 

[Ande]

what's the reasoning behind the 12v "conditioner" ?

Placebo and superstition.
There is no "conditioning" an old PB battery.
You can save a few charge cycles by connecting an charger/power supply that maintain higher voltage (reducing the chemical reactions of dis/recharging)

Also, depending on the way the electronics monitor the 12v battery, doing so over some time, may trig an alarm due to unusual charge statistics.

 

[travellerva]

Thanks everyone for your suggestions and help. However, maybe I should have been more clear in my question. Regardless of whether using a battery trickle charger is wise or not, my puzzlement is that the battery charger shows the battery as being quite healthy whereas the MS software says it needs to be replaced. This particular battery was replaced 16 months/8,000 miles ago so it is unlikely to be in poor shape.

So is it possible the MS software is 'reading' something incorrect about the battery? Is there some other test I can run to check on its condition?

By the way, I have tried rebooting both software systems a couple of times with no effect.

 

[Snerruc]

It’s more likely your charger is giving the wrong information. Your car is looking at the voltage drawdown and other factors under different loads. It is a lot smarter than your charger. Batteries are cheap compared to breaking down in rush hour traffic on the interstate.

 

[scottm]

Gen1 cars, prefacelift, when parked for long periods will need to recharge the 12v battery about 8 times a day (24 hrs) by closing main pack contactors and DC-DC charge the 12v then disconnect. Deep cycles like this are what kills the battery.

Keeping a trickle charger on the 12v keeps it floating and powers vampire drains in the car, so the battery doesn't cycle at all. Longer life for the 12v.

I keep my S on trickle all the time it's in my garage, even just for overnight, and I seldom charge main pack at home. My original 12v lasted 4.5 years which is on the high side.. when lots of people are doing these every couple years.

In case you're wondering, the 12v doesn't cycle while driving or while charging the car. Because the contactors are closed during these times and the DC-DC converter is floating the 12v... just like the trickle charger does in my garage.

Finally, facelift cars don't have the same concern with 12v battery. They've rewired these cars so the DC-DC converter is always live, its now directly connected to the hot side of the contactor. So the 12v is constantly trickling from the main pack. Tesla finally got it right in 2016.

 

[travellerva]

Let me try again with my question.

Is it reasonable that a new 12V battery should need replacement after only 16 months and 8,000 miles?

This is on a 2014 MS 85. The first 12V battery lasted 4 years. Neither my driving patterns or charging routines have changed.

 

[dblankenbaker]

Disconnect the negative post on the 12v battery.

Wait a few minutes for good measure.

Reconnect the 12v battery and your car will think you replaced the battery.

Everything will be fine.

 

[Tam]

...Neither my driving patterns or charging routines have changed.

Could that be that after you introduced the battery conditioner to your car and coincidentally, this happens?

 

[ucmndd]

Disconnect the negative post on the 12v battery.

Wait a few minutes for good measure.

Reconnect the 12v battery and your car will think you replaced the battery.

Everything will be fine.

This, except power down the car first.

If the message was a transient reading issue due to your use of a battery tender, it will go away and not come back.

If it comes back, the battery likely does have an issue.