Any reason not to hook up a battery tender to the 12 volt battery ?

[iCharge]

To avoid 12V cycling, you need a tender that can provide about 50 watts -- at 12V, that's a tad over 4A. There are many recommendations on this thread for suitable 12V tenders of that specification. I popped the nose cone, connected some terminals to the battery posts, routed them inside the "frunk" of my classic P85+. I drive a lot too (~70k miles in ~4 years), and I'm still on the original 12V, 4.5 years later. I've probably jinxed myself for posting this ;-)

@SteveS0353 Thank you so much for your helpful input. Can you kindly share where the 50 watt number is from ? Did someone test the load somewhere or in this forum ?

 

[iCharge]

I would not run a 12V lithium in NE (or anywhere with extreme winters). The battery will fail quickly when charged below freezing.

True that, I am already seeing 32s around here and its just November !

 

[iCharge]

When driving, the traction battery provides all of the energy, including charging the 12V; you are not draining the 12V while driving despite the extra "widgets".

Also, 12V batteries were not designed for very thirsty vampire drain when parked. Calculations indicate that the vampire drain on the 12V is roughly equivalent to a 40 watt incandescent lamp running continuously. No ICE car has that sort of drain on the 12V when parked. There is s wide variance in MTTF on Model S vehicles, but the statistics indicate that early Model S vehicles had 12V battery replacements about every 12-18 months. The battery type has changed, and the vampire has been made less thirsty, and more recent vehicles have been reporting 3+ years MTTF. But that does not avoid the fact that the cycle based wear out of even the more recent better deep cycle AGM batteries will eventually bring their demise.

hey do you [ or anyone else out here ] have any thoughts on which is preferable
https://www.amazon.com/dp/B01BM51QD6?tag=slicinc-20&ascsubtag=90d6bc02e11811e89e79ea7718e137e00INT
- provides more than 5Amp that is mentioned as drain on the deep cycle battery
- cheaper
- ? not many reviews on maintainer function
- ? too much power harmful ?
My personal opinion based on no evidence is that this will be more than enough to supply the 'vampire drain' components of the Model S to prevent any discharges of the 12V and even if it does, it has enough power to "rapidly charge" it back to 12V AGM. At best either eliminating the deep cycling and at least reducing the time battery will spend at lower charge.
Also is this rapid charge going to be *bad* for a LA battery ?

Alternatively
product from battery tender
https://www.amazon.com/Battery-Tend...p/B00EDFPN1O?ref_=bl_dp_s_web_2582981011&th=1
- 5 Amp = just enough but underpowered as currently Tesla charges at 6.5 - 7 Amp per Russell's research
- reputed seller
- plenty of reviews = reliable
I *feel* this is barely enough or more correctly not enough, and may not be able to prevent the discharge when the computers etc need power, that is the battery *will* cycle, it shall bring it back to 12V a little slower than without it hooked and [hopefully] without drawing power from traction battery but the latter is less of my concern.

any thoughts and input is deeply appreciated.

 

[whitex]

You can argue that we don't have a good sample set, but it just common knowledge that a lead acid battery will wear out faster with cycling than sitting on a float charger. The deeper the cycling, the more the wear/shorter the life.

I think the problem is that the "common knowledge" is for deep cycling. Teslas top off often, so its "shallow cycling" which is unique to EVs.

 

[whitex]

I have a number of sports cars that are occasionally driven and are on CTEK 12V battery maintainers... all with 10+ year lifespan.

I had a Lexus hybrid which I only drove about 44K miles in almost 8 years before the 12V battery needed replacing - no tenders or external chargers. I also had a Toyota Sienna which needed a new battery after 3 months, apparently defective battery because the replacement lasted 5 years or longer (sold the car with it).

 

[tga]

I think the problem is that the "common knowledge" is for deep cycling. Teslas top off often, so its "shallow cycling" which is unique to EVs.

Per measurements here, it looks like the battery is run down to ~12.35V, or ~50%SOC. This post calculates 1800 50% cycles, or about 18 months, before the stock battery hits its cycle limit.

 

[whitex]

Per measurements here, it looks like the battery is run down to ~12.35V, or ~50%SOC. This post calculates 1800 cycles, or about 18 months, before the stock battery hits its cycle limit.

The first post calculates 3 cycles per day by dividing the vampire loss by the battery capacity, which would only be true if the battery was deep cycling down to empty.

Typically, the vampire load is 1.2kWh per day.
[...]
The above battery had a capacity of 33 ampere-hours (33AH on the label). At 12V this is 0.396kWh of capacity. The 1.2kWh vampire load represents 1.2 / 0.396 = 3 charge / discharge cycles per day.

That is also assuming 100% efficiency, but let's ignore that for this post as it doesn't change the number that much as long as it's not too inefficient. If we assume the above numbers are correct but Tesla discharges to 50% instead of 0%, that's 6 cycles per day, not 3.

The poster later states that he read the capacity chart for the battery to be capable of 1800 100-50% cycles.

Assuming Tesla allow the 12V battery to discharge 50% before recharging it from the DC-DC converter, the battery has a cycle limit of 1,800 before wear out. At 3 cycles per day, the 12V battery in the Model S would have a typical lifetime of 600 days, or ~18 months.

If we plug the correct 6 cycles instead of 3 cycles per day into the above, the post predicts majority of battery failures only 9 months after production, which we know is not what majority of people are experiencing, hence obviously either the logic, or data used in the logic, is wrong. My guess, besides the mistake in the cycles per day calculation, that the manufacturer data mat not be right as EV usage (slow discharge cycling) has not been studied by the manufactures (for example, an ICE starter draws 50A-100A from the battery, which is a shock to a battery and likely adds to the wear - this never happens in a Tesla).

Bottom line is this, I don't really feel the need to keep going though a bunch of quoted posts, pointing out calculation or logic mistakes, to try to prove that we don't have good data supporting that that a battery tender extends a life of a 12V battery in a Tesla beyond it's natural expected end-of-life due to age. Use battery tenders if that makes you feel better, it's not going to hurt as long as the tender itself is not faulty (meaning it doesn't interfere with car electronics and/or doesn't overcharge the battery which would cause premature failure) and and you don't accidentally short out the battery when connecting and disconnecting it. Personally I just plan to replace my 12V battery after 5 years or so (unless it dies earlier) since I prefer to have a reliable battery onboard, and even car battery manufacturers won't warranty them beyond 5 years (often just 3 years), which means that is the lifetime the battery was designed for - you can of course get more but at lower expected reliability.

 

[FlatSix911]

hey do you [ or anyone else out here ] have any thoughts on which is preferable
https://www.amazon.com/dp/B01BM51QD6?tag=slicinc-20&ascsubtag=90d6bc02e11811e89e79ea7718e137e00INT
- provides more than 5Amp that is mentioned as drain on the deep cycle battery
- cheaper
- ? not many reviews on maintainer function
- ? too much power harmful ?
My personal opinion based on no evidence is that this will be more than enough to supply the 'vampire drain' components of the Model S to prevent any discharges of the 12V and even if it does, it has enough power to "rapidly charge" it back to 12V AGM. At best either eliminating the deep cycling and at least reducing the time battery will spend at lower charge.
Also is this rapid charge going to be *bad* for a LA battery ?

Alternatively
product from battery tender
https://www.amazon.com/Battery-Tend...p/B00EDFPN1O?ref_=bl_dp_s_web_2582981011&th=1
- 5 Amp = just enough but underpowered as currently, Tesla charges at 6.5 - 7 Amp per Russell's research
- reputed seller
- plenty of reviews = reliable
I *feel* this is barely enough or more correctly not enough, and may not be able to prevent the discharge when the computers etc need power, that is the battery *will* cycle, it shall bring it back to 12V a little slower than without it hooked and [hopefully] without drawing power from traction battery but the latter is less of my concern.

any thoughts and input are deeply appreciated.

I have owned a number of battery chargers over the years and have found the CTEK line to be superior...

Take a look at the product link and marketing information here https://www.amazon.com/CTEK-56-353-...e&ie=UTF8&qid=1541478837&sr=1-3&keywords=ctek

 

[FlatSix911]

Here is an updated Amazon review of the Best Battery Chargers

 

[Bill D]

Whether or not leaving a Tender hooked up extends 12V battery life, it may extend main battery life.

We're often out of town for months with both our MS on HWPCs. Their main batteries cycle somewhat because the charging of their 12V batteries passes through them. The amount of cycling is magnified by the multi-step inefficiencies.

Admittedly, those main battery cycles are small compared to normal daily driving, but eliminating them may be helpful.

 

[iCharge]

Whether or not leaving a Tender hooked up extends 12V battery life, it may extend main battery life.

We're often out of town for months with both our MS on HWPCs. Their main batteries cycle somewhat because the charging of their 12V batteries passes through them. The amount of cycling is magnified by the multi-step inefficiencies.

Admittedly, those main battery cycles are small compared to normal daily driving, but eliminating them may be helpful.

exactly my point, but as you can see, my thoughts have not had much traction here. and other than @FlatSix911 , I have not had any suggestions on which one they are using :-\

 

[brkaus]

exactly my point, but as you can see, my thoughts have not had much traction here. and other than @FlatSix911 , I have not had any suggestions on which one they are using :-\

I think it’s worthwhile for a car that would sit for a while, say a few days/weeks at a time.

I don’t think it’s worth the trouble for every day. And I’d be the first to drive off and rip the wire out because I forgot.

I have a ctek charger and it’s my favorite charger.

 

[iCharge]

I think it’s worthwhile for a car that would sit for a while, say a few days/weeks at a time.

I don’t think it’s worth the trouble for every day. And I’d be the first to drive off and rip the wire out because I forgot.

I have a ctek charger and it’s my favorite charger.

how many amps output on your CTEK ? or if you can share the model number that'd be great

 

[iCharge]

That unit puts out 4.3 Amps, so it might be just enough for the incredibly thirsty Vampire in the MS if it is connected continuously, but there is also the problem that the MS disconnects the 12V CLR from the 12V battery after 10-20 minutes and then there is no way for this unit to charge though the CLR.

Thanks, I was able to snag the NOCO Genius 7.2Amp on their Black Friday Special

 

[iCharge]

a switching power supply that converts 400VDC to 12VDC is a trivial thing--there's one in the car already to charge the12VDC battery. Functionally the same thing as the external trickle chargers you're suggesting. Why doesn't tesla run the 12VDC components off of that and dispense with the 12V battery?

No engineer capable of doing any part of this would overlook that possibility unless there was a darned good reason. My guess is that the 12VDC loads fluctuate wildly and the worst case is several tens of amps. They chose to go with a small trickle charger and a bigger lead battery. That's probably a bunch cheaper than having a 12VDC power supply big enough to supply the worst case 12V load and is available off the shelf.

my guess is that the external trickle chargers won't help the problem at all....if they do, simply building a slightly bigger trickle charger into the car than the one that's already there would solve the problem trivially and telsla would have already done it. my guess is that they're working on whatever the loads are that give the 12V system a hard time but that they're proving challenging. do any of the folks that have put current monitors onto the 12VDC system have any thought what they may be?

--Snortybartfast

a switching power supply that converts 400VDC to 12VDC is a trivial thing--there's one in the car already to charge the12VDC battery. Functionally the same thing as the external trickle chargers you're suggesting. Why doesn't tesla run the 12VDC components off of that and dispense with the 12V battery?

No engineer capable of doing any part of this would overlook that possibility unless there was a darned good reason. My guess is that the 12VDC loads fluctuate wildly and the worst case is several tens of amps. They chose to go with a small trickle charger and a bigger lead battery. That's probably a bunch cheaper than having a 12VDC power supply big enough to supply the worst case 12V load and is available off the shelf.

my guess is that the external trickle chargers won't help the problem at all....if they do, simply building a slightly bigger trickle charger into the car than the one that's already there would solve the problem trivially and telsla would have already done it. my guess is that they're working on whatever the loads are that give the 12V system a hard time but that they're proving challenging. do any of the folks that have put current monitors onto the 12VDC system have any thought what they may be?

--Snortybartfast

Thanks for your thoughtful suggestions.
In my limited knowledge of electronics incl LA batteries [=LAB], I am of the understanding that the life of LABs is dependent on their health, which is worn out by few factors

1. State of Charge [ low = shorter battery life ]
   
2. Number of (deep) discharge cycles [ high = shorter battery life ]
   
3. (Sustained storage at) Temperature [ low = short battery life ]
   
4. Time spent at deeply discharged state [ more = shorter battery life ]

With that in mind, and information from Russell Graves at Syonyk's Project Blog: Tesla Model S 12V Battery Analysis ( full disclosure, I did exchange a few emails with him on this topic) it appears that the 12V in a Tesla MS goes through multiple deep cycles many times a day and is then topped by the Traction battery [TB]

Personally, for me, the above combined with the fact that my MS sits in a non heated garage [ today the temperature was negative 10 degree Celsius in my garage ] and is driven an average of 1x/week in winter, it makes sense to me to hook the 12V Batt to a external Charger with 2 potential advantages:

1. for the 12V Battery: If the external charger can supply all the amps for whatever drains it, this will decrease number of discharge / charge cycles, and it cannot supply all the power, it'll lower the depth to which it discharge. In case of latter, it'll take less time for TB to bring it to optimal voltage and this will reduce the amt of time 12V spends at lower level of charge. All of these will lead to less TB discharge
   
2. Lessen Vampire Drain on the main TB and hence preserve range

some one made an argument that one could just 'plug the car in' and let the car do its thing, which only solves [2] above and though acceptable but does not prevent the discharge cycles on the 12V.

I plan to keep my MS for as long as I can, so I see no disadvantage to hook it to a Battery Tender. After much research I got a NOCO 7.2Amp unit.

If anyone had any critique on above or ideas on how to measure TB drain automatically or to see if this intervention had any outcome with hard data, I am open to suggestions and a constructive discussion

 

[rrolsbe]

Thanks for your thoughtful suggestions.
In my limited knowledge of electronics incl LA batteries [=LAB], I am of the understanding that the life of LABs is dependent on their health, which is worn out by few factors

1. State of Charge [ low = shorter battery life ]
   
2. Number of (deep) discharge cycles [ high = shorter battery life ]
   
3. (Sustained storage at) Temperature [ low = short battery life ]
   
4. Time spent at deeply discharged state [ more = shorter battery life ]

With that in mind, and information from Russell Graves at Syonyk's Project Blog: Tesla Model S 12V Battery Analysis ( full disclosure, I did exchange a few emails with him on this topic) it appears that the 12V in a Tesla MS goes through multiple deep cycles many times a day and is then topped by the Traction battery [TB]

Personally, for me, the above combined with the fact that my MS sits in a non heated garage [ today the temperature was negative 10 degree Celsius in my garage ] and is driven an average of 1x/week in winter, it makes sense to me to hook the 12V Batt to a external Charger with 2 potential advantages:

1. for the 12V Battery: If the external charger can supply all the amps for whatever drains it, this will decrease number of discharge / charge cycles, and it cannot supply all the power, it'll lower the depth to which it discharge. In case of latter, it'll take less time for TB to bring it to optimal voltage and this will reduce the amt of time 12V spends at lower level of charge. All of these will lead to less TB discharge
   
2. Lessen Vampire Drain on the main TB and hence preserve range

some one made an argument that one could just 'plug the car in' and let the car do its thing, which only solves [2] above and though acceptable but does not prevent the discharge cycles on the 12V.

I plan to keep my MS for as long as I can, so I see no disadvantage to hook it to a Battery Tender. After much research I got a NOCO 7.2Amp unit.

If anyone had any critique on above or ideas on how to measure TB drain automatically or to see if this intervention had any outcome with hard data, I am open to suggestions and a constructive discussion

iCharge

What mode did you set your NOCO G7200 when you connected it to the battery. I connected my G7200 to my Model 3 battery and set it to the 12 Cold/AGM mode and the charger never topped off the battery. In this mode, the charger is supposed to top off the charge when the battery terminal voltage reaches 12.8V +/- 0.2V. I have a Kill-O-Watt meter and the G7200 AC line is being monitored by it. It only drew 20 watts over a 12 hour period so I know it did not top off the battery. The car however did top off the battery when the voltage across the terminals got below 12.7 volts probably closer to 12.6V. The power supply mode outputs 13.6V and appears to be supplying the Phantom current the car requires. After the Model 3's DC-to-DC converter completes the top off cycle the voltage at the battery terminals is 13..6V. Using the power supply mode, I am not sure the charger will back off if the cars DC-to-DC converter kicks in (ie.. the drivers door is opened or the phone app accesses the car); likewise, the G7200 charger does not remember the power supply mode setting and must be manually enable after losing AC outlet power. I think power supply mode would not overcharge the battery but simply maintain 13.6V and should also deliver the power required for the Phantom drain. Even if the G7200 topped off the battery at around 12.8V, it would still be cycling the 12V battery thus reducing it useful live. If the charger could just keep the battery topped off, supply needed Phantom current and not require the traction battery/DC-to-DC converter to top off the 12V battery, that would be ideal. I calculated the approx power usage using the power supply mode and it appears to be less than 9KW/month as apposed to over 30KW allowing the car to maintain the 12V battery. The traction battery should theoretically not loose any range even if parked for several weeks.

 

[N..8]

RRolsbe, I have the same set up as you do and I just plug it in and let the NOCO do it's thing. I don't change it to Cold/AGM, just plug it in. I see about 120watts being pulled a few times a day. Over a 3 day period it will use about 1.2kw. I believe the DC to DC doesn't kick on until the battery gets to 12.6 or 5. If my car is sleeping is doesn't loose any over 3 days, this is the longest my car was sleeping at one time. Once it's awake it will over power the NOGO I believe then does engage the DC to DC.

 

[rrolsbe]

RRolsbe, I have the same set up as you do and I just plug it in and let the NOCO do it's thing. I don't change it to Cold/AGM, just plug it in. I see about 120watts being pulled a few times a day. Over a 3 day period it will use about 1.2kw. I believe the DC to DC doesn't kick on until the battery gets to 12.6 or 5. If my car is sleeping is doesn't loose any over 3 days, this is the longest my car was sleeping at one time. Once it's awake it will over power the NOGO I believe then does engage the DC to DC.

Thanks for the reply!

When you just plug it in, what LED lights are illuminated on the NOCO G7200 charger? I had to close the Frunk latch by pushing down on the latch with a screwdriver so I can keep the Frunk open (the car thinks it is closed). This allows me to monitor the battery voltage and current draw with a DC current probe. Before I closed the latch with a screwdriver, my Model 3 would not go to sleep.

Thanks Again, Ron

 

[travellerva]

How do you get to the 12v battery to hook up the battery charger? What do you have to take off, etc?

A couple of times on this thread, members have asked a basic question: "How do hook up a battery tender to the 12V battery?" but the answers have not been detailed enough for newbies like me - not a newbie to Tesla, just to the forum.

I've owned a 2014 MS 85 since new that now has only 35K miles on it. The 12V battery is the original. I'm going away for 3 months soon and after reading this thread, I want to leave the 12V battery on a tender as well as the car being plugged in to the HPWC just to cut down the recycles on the 12V battery. As I see it the only way to get at the 12V battery is by removing the front nose cone. When I do that, all I see is a +ve terminal (see pic) so I assume any -ve connection from the tender will just have to latch on to the car frame anywhere - correct? Is there some other easyView attachment 371505 way of removing the frunk lining to get a connection to the battery and just string the tender cable out of the frunk lid? I'd like to make it possible to use the tender in the future more frequently and having to pulling off the nose cone every time doesn't excite me.

Thanks for help.

 

[Kenz]

Just plug the car into a normal household outlet 110 with the mobile charger that comes with the car and forget about it.