Replacing the 12V aux Battery

[shrink]

Got the dreaded "Aux Battery Supply Low" message today. I actually find this remarkable because I've owned the car exactly for exactly 3 years today, I live in a desert, and this is the first time I'm getting this message. I did not think the battery would last 3 years in these conditions.

Anyone have any ideas or guesses on how much juice is left when this message comes up? I don't want to get stranded, but I am taking it up to Tesla Service today. Luckily it's apparently covered under my CPO warranty, which expires in 30 days.

 

[glight2000]

You

Got the dreaded "Aux Battery Supply Low" message today. I actually find this remarkable because I've owned the car exactly for exactly 3 years today, I live in a desert, and this is the first time I'm getting this message. I did not think the battery would last 3 years in these conditions.

Anyone have any ideas or guesses on how much juice is left when this message comes up? I don't want to get stranded, but I am taking it up to Tesla Service today. Luckily it's apparently covered under my CPO warranty, which expires in 30 days.

You can go quite awhile with the low aux battery warning. I think I went for a month before I tapped out with frustration of no music. The only problem is the delay in unlocking the doors. I never needed to use the opening charge door trick.

 

[shrink]

You


You can go quite awhile with the low aux battery warning. I think I went for a month before I tapped out with frustration of no music. The only problem is the delay in unlocking the doors. I never needed to use the opening charge door trick.

That's really good to know! I'll keep that in mind for next time. Got my new battery today, though, under my about to expire CPO warranty so I'm quite pleased.

I'll be shocked if this new 12V battery lasts another 3 years in Phoenix.

 

[Jonathanm]

I'm going to give one of these a try....not bad for €70!

Batterie moto Skyrich Lithium Ion YTX9-BS

 

[n2mb_racing]

Over a year now I think. The shorai I used has been faultless.

Perrin21, is the battery still working well? Part number is LFX09L2-BS12 , right?

 

[Stefan T]

Mine is still working and that's over 2 years since swap mine

 

[n2mb_racing]

Mine is still working and that's over 2 years since swap mine

Cool. Which battery?

 

[Stefan T]

Shoai LFX09L2-BS12

 

[n2mb_racing]

Shoai LFX09L2-BS12

Some kind of Tesla mind trick... Just as I was talking about this, my service manager contacted me to say they got the 12V warning message while doing my annual service. So, time to replace the 12V battery! Looks like I'll go with the Li-Ion.

 

[n2mb_racing]

I was researching this some more and realized that the Shorai LFX09L2-BS12 doesn't include any kind of BMS to balance the cells. It seems like in the intended motorcycle application, they expect that once in a while you will use their external balance charger to charge the battery and balance the cells.

I emailed Shorai to see if this would be fine in a long-term application where it would be only be charged by the +12V connector. They said it would self-balance (internal balancer?) when the cells are above 14.6V and that the battery should not fall below 12.86V resting state (20%).

Does anyone remember the Roadster 12V charger parameters? What voltage it kicks on at and what it charges to?

 

[gregd]

I was researching this some more and realized that the Shorai LFX09L2-BS12 doesn't include any kind of BMS to balance the cells. It seems like in the intended motorcycle application, they expect that once in a while you will use their external balance charger to charge the battery and balance the cells.

I emailed Shorai to see if this would be fine in a long-term application where it would be only be charged by the +12V connector. They said it would self-balance (internal balancer?) when the cells are above 14.6V and that the battery should not fall below 12.86V resting state (20%).

Does anyone remember the Roadster 12V charger parameters? What voltage it kicks on at and what it charges to?

I've not done a long-term study on the 12v system, but I don't recall the voltage ever going above about 13.8v, nor much below that either. It seems to just rest there, trickle-charging the battery instead of cycling it like a gas car does. This is all with the front hood open, but it seems to stay there even when the car goes to sleep (pump and Acc outlet turn off). I have no idea what's keeping it at that voltage when the contactors are not engaged, nor what conditions would cause it to not do that.

When I got my 12v battery replaced a couple of years ago (the car warned me it was weak), I had the SC bring a pair of wires up to the top of the front compartment, terminated with a PowerPole connector. The idea is that I can "jump start" the car if it goes flat on me (though it never has). But it also provides a convenient point to measure the battery directly without disassembling the car. The 12v Accessory outlet measured 13.5v just now (car awake but not key-on) with the battery at 13.8, so there's something active between the two, i.e. not just a relay or the Ign switch like on an old ICE. Likely also means you can't back-charge the 12v battery through the accessory outlet.

 

[snd92]

My 12 V battery rest at 11.5-11.6 V and once the car is "ON" it jumps to 13.6-13.7. I don't know if this is normal. The battery was replaced approx. 1 year ago by Tesla.

At least that is what I measure from the Alarm fuse, which is connected (tapped) to my dashcam.

 

[Stefan T]

My 12 V battery rest at 11.5-11.6 V and once the car is "ON" it jumps to 13.6-13.7. I don't know if this is normal. The battery was replaced approx. 1 year ago by Tesla.

At least that is what I measure from the Alarm fuse, which is connected (tapped) to my dashcam.

If your battery voltiage is so low on a lead acid battery used on a fossil car it had not start and need to be replaced or charged

 

[snd92]

What do you measure from fuse 13 when car is on/off?

 

[gregd]

My 12 V battery rest at 11.5-11.6 V and once the car is "ON" it jumps to 13.6-13.7. I don't know if this is normal. The battery was replaced approx. 1 year ago by Tesla.

At least that is what I measure from the Alarm fuse, which is connected (tapped) to my dashcam.

Interesting. I brought the wires from the battery out from under the hood (so I could close it fully), unplugged the car, and left it for 2 days. The 12v accessory outlet is definitely off. Also made sure the GSM radio is set to Off. I can't think of any reason the car would be awake, but the 12v battery still measures at 13.77v.

I don't have a tap on the Alarm fuse, so can't measure it there. Other than that, what are you doing different from me?

 

[n2mb_racing]

I measured mine this morning and the battery read 13.6V. I believe I have leads direct to the battery, but I'm not sure since the previous owner installed them. The coolant pump was running, so the car was awake, but key off. I was thinking I might log it over 24-48 hours using data recorder.

 

[snd92]

@gregd and @n2mb_racing, When measuring after unlocking/turning VDS on (with coolant pump running) I get 13.6-13.7 V. After the bzzz sound is turned off (coolant pump off) I get 11.5-11.6 V. Once unlocking again or touching VDS it raises to 13.6-13.7 V.

@gregd, depending on the fuse you'll be able to measure the voltage with the fuse on or by pulling the fuse off.

 

[ML Auto]

The battery is connected to the APS thru the switchpack, and is charged whenever the car is awake. The output voltage from the APS is 13.5V.

 

[gregd]

The battery is connected to the APS thru the switchpack, and is charged whenever the car is awake. The output voltage from the APS is 13.5V.

Ok, so why am I seeing 13.8v from a set of wires that are supposedly going direct to the 12v battery, even when the car appears to be asleep? Choices:

1. The car isn't going to sleep, even though the pump goes off and the cabin Acc outlet and VDS both go dark.
2. The wires that the SC installed for me when they replaced the battery don't actually to to the battery, but to some other source of 13.8v that stays on all the time.
3. The battery is connected (incorrectly) to some constant 13.8v source instead of what it's supposed to be connected to, and I'm just reading that via the wires which properly do go to the battery.
4. The APS / Switchpack is defective and outputting the 13.8v even when the car is asleep.
5. Something else?

I'm assuming your 13.5v and my 13.8v are in fact the same, and it's a tolerance or measurement accuracy difference (I'm using a Radio Shack 22-809 Pocket DMM, not a lab bench meter). But, maybe that's another clue...

I know some of these are "impossible", for example #4 - aren't the 2.0 cars totally inert (no power anywhere) if the 12v battery is disconnected and the traction contactor is not engaged? I do believe (audibly) that the contactor is out when the car is asleep, so no other source of power to feed the APS / Switchpack, right? Or do the 2.0 cars also have a voltage tap into the ESS separate from the traction feed, like the 1.5's?

Stumped.

 

[n2mb_racing]

So, I guess the charging behavior is different than on the Model S? I remember reading that the 12V battery charging on the Model S kicks in at some minimum voltage and then stops at some maximum voltage, and that voltage cycling repeats 4-5 times per day. Does the 12V battery not drain and recharge as often on the Roadster?