Installing a 12v 5amp Battery Tender to the 12v Battery on 2016 Tesla Model S P90D

[chrissmith007]

I do not work for Tesla; I am not a mechanic; I am not promoting doing this; do at your own risk:

I have a 2016 Model S P90D. I installed the quick connect cable directly to the 12v battery (purchased on amazon called, "SPARKING 6FT Ring Terminal Cable - SAE to O Ring Terminal Harness Quick Connect/Disconnect Ring Terminal Assembly, 10A Fuse-6FT). This is the same way that I have done for years with my motorcycles and other cars. When you have the tub removed from the frunk its very simple (4-6 screws to remove; look on YouTube). With the tub removed I drilled a hole in the plastic tub and the material tub liner insert for the battery tender connection cable to go through and just sit inside the frunk when not used. I then purchased a 12 v 5 amp Battery tender charger (I initially had the 12 v 1.25 amp battery tender for my motorcycle but I read on the tread that you need more amps. It did work and charged the battery but the 5 amp works way faster). I can still close the frunk while it charges without pinching wires. Works great. 12v battery was on solid green within 10 min. Later I installed a more fancier style docking port for the battery tender to just plug into called a
"Kohree SAE Power Socket Sidewall Port Connector" purchased on Amazon.

The main thing to remember not to do is to not drive off while you still have the battery tender still plugged in. Its not like the main battery that wont allow you to drive or send you a warning message. There is no warning message.

I am making a YouTube video not to encourage this or to promote doing this. This is at your own risk.
YouTube Video that I made:

 

[eladts]

Can you explain the purpose of such modification? Battery tenders make sense if you want to keep the 12v battery of an ICE car without turning on the engine. Why would you need it in an EV that charge the 12V battery from the main battery?

 

[chrissmith007]

Can you explain the purpose of such modification? Battery tenders make sense if you want to keep the 12v battery of an ICE car without turning on the engine. Why would you need it in an EV that charge the 12V battery from the main battery?

The 12v battery life is not very long. If you don't get to drive your Tesla much due to travel or if you park for long periods of time for work trips or vacations or If you own and drive other vehicles and your tesla sits then the 12v battery will die in 7 months to a year. The less you drive it the faster your 12v battery will die. There are a few strings here that owners mention replacing the battery every other year. I did this to extend the life of the 12v since I travel a lot and the car sits. Even with daily use the car drains the 12v battery using all the many features such as the door handles opening and closing, the mirrors opening and closing, the computer communicating to wifi or your cell phone, etc. Many have experienced the 12v battery die and they needed to jump start the battery. Others receive a warning message about the 12v battery but after the warning there is no indication of how much time you have remaining until total loss of power and once its out then nothing will function. It was a low price modification that cost under $90. It was $65 for the 12v 5amp battery tender, $12.38 for the sidewall port connector, and $10.99 for the 6ft terminal cable. My first 12v battery replacement was free under warranty, however the next one will not be covered under warranty. The 12v batteries are very expensive and only available through Tesla based on size and terminal port configuration. Others have did trial and error using other type battery brands and sizes but they didn't fit or had other issues trying to screw the Tesla battery terminals in to the non tesla battery. My project is simply an experiment to see if I can extend the battery life longer than relying on the regenerative features of letting the vehicle charge the battery while driving. Many others on TMC Forum are doing this and its working. This is just another way that I am sharing.

 

[Watts_Up]

- Interesting idea and clean solution for any car not used daily to prevent battery drain.
Especially since nowadays, 12 V batteries are only warranty for 2 years.

- This is for the Model S, but don't you think that this was improved on the Model 3?
I put a voltmeter on my auxiliary plug and I noticed that the voltage stays around 13 V, and jump to 15 V when recharging.
But I imagine that there is no 12 V charging when the car is sleeping.

With the tub removed I drilled a hole in the plastic tub and the material tub liner insert for the battery tender connection cable to go through and just sit inside the frunk when not used.
I can still close the frunk while it charges without pinching wires.
Later I installed a more fancier style docking port for the battery tender.

The main thing to remember not to do is to not drive off while you still have the battery tender still plugged in.
Its not like the main battery that wont allow you to drive or send you a warning message. There is no warning message.

- Why really making a hole and exposing the plug to the elements when driving?
If you are at home, why not keeping your frunk ajar, so you will get a warning if you try to start your car.

- Otherwise, why not making your wire going inside all the way to the rear of the car, so your tender will be next to the DC charger,
so you will not forget to go to the front of the car to disconnect the tender. Especially if you have more than user of the car.

Note: I have a charger for my other car and a way to remember to disconnect the charger is to put a piece of paper in front of the tachometer.

 

[Uncle Paul]

The 12 volt battery is usually charged by the huge traction battery when it is needed. Little need for a trickle charger.

 

[zzf00l]

Well you learn something every day on here.. I imagined that the large battery kept the 12v battery fully charged, even when parked up!

 

[murphyS90D]

If you connect a real smart battery charger to the 12 volt battery there will be no loss of charge in the HVB. The car lets the 12 volt battery drop to 50% SOC before recharging it. This is the source of "vampire drain". A smart battery charger keeps the battery topped off without the large swings in SOC.

I installed a fused battery connector in my car shortly after I got it. My car is a 2016 pre-refresh. The connector is mounted to the top of the steel cross beam using existing threaded holes. It is easily accessible by popping the nose cone off.

 

[chrissmith007]

- Interesting idea and clean solution for any car not used daily to prevent battery drain.
Especially since nowadays, 12 V batteries are only warranty for 2 years.

- This is for the Model S, but don't you think that this was improved on the Model 3?
I put a voltmeter on my auxiliary plug and I noticed that the voltage stays around 13 V, and jump to 15 V when recharging.
But I imagine that there is no 12 V charging when the car is sleeping.


- Why really making a hole and exposing the plug to the elements when driving?
If you are at home, why not keeping your frunk ajar, so you will get a warning if you try to start your car.

- Otherwise, why not making your wire going inside all the way to the rear of the car, so your tender will be next to the DC charger,
so you will not forget to go to the front of the car to disconnect the tender. Especially if you have more than user of the car.

Note: I have a charger for my other car and a way to remember to disconnect the charger is to put a piece of paper in front of the tachometer.

These are excellent suggestions that I will follow to prevent accidentally leaving plugged in.

I will not be charging my 12v battery daily or not frequently so I will need to remember your suggestions. I plan to only do this when I will be leaving my vehicle for long periods of time unused. In the colder months or seasons is generally when owners have reported the 12v battery issue.

I chose this mounting location for the 12v battery charging because it’s convenient for the location in my garage for how I front end park and where my nearest plug is located and the area that I always look before I get into the car to glance at my motorcycle. However, when I am not charging or conditioning my 12v battery I store the battery tender in the frunk as I do not keep anything else in the frunk. But leaving the hood open makes perfect sense.

With this experiment I hope to be able to report if this will help prolong the 12v battery life in hopes to save the environment, money, and battery replacement/installment time as well as help thousands of other vehicle owners who will experience needed to deal with this every two years.

This is my second Tesla model S. I’ve owned a 2012 and now 2016. The 2012 was still in perfect condition and would have driving and worked for many more years to come. I only traded it to experience the newer and more Moderized features. I have put down a $100 deposit on the Cybertruck however, I hope that I can afford to keep my model S when the cybertruck is finally available. It will be amazing to own both but if I can’t that will be the only reason that I will trade in my model S.

Tesla’s are amazing and I haven’t missed a gas combustion noisy/loud oil dripping car since. EV’s are the Future. I wish more people would get onboard and stop producing gas cars. There are enough already made to enjoy without making more. Oil, gas, transmission fluid, power steering fluid, coolant, etc all needed for combustion vehicle. It doesn’t make sense when you think about it all. Go clean. Go Tesla!!

 

[N4HHE]

If you connect a real smart battery charger to the 12 volt battery there will be no loss of charge in the HVB. The car lets the 12 volt battery drop to 50% SOC before recharging it. This is the source of "vampire drain". A smart battery charger keeps the battery topped off without the large swings in SOC.

What voltage does the Model S allow the 12v battery drop before the 12v inverter kicks in?

What voltage is the cutoff?

My 2013 has been cycling 24/7 every 2-15 minutes when parked. Put volt meter on a hot fuse and found 14.14v peak, contactors clack, then voltages falls to 13.50v, then contactors clack again, voltage rises to 14.14 for a while then cycle repeats. Burns about 8 miles/day.

Using TeslaFi‘s guide for getting a Tesla to sleep did what I could yesterday. Car finally slept 8 hours later. Still asleep. Brought wires out the hood to monitor without having to open the trunk. New Ohmmu is 13.26v all day. Mobile Connector is on 120v with a Kill-A-Watt monitoring. Has drawn 0.02A (1.7W) continuously past 24 hours (normal for a Mobile Connector). That is excellent. I’d have to wake the car to check traction battery SOC.

Sean at Ohmmu has been very helpful but he says it should start charging at 13.0 and kick off at 13.5. Mine was starting at 13.5 and kicking off at 14.14 or higher.

My observation of battery maintainers is they hold 13.0 for a week or two then let it drop to 12.6. And some time later kick it back up. Haven’t kept one sit long enough to see but have read the literature on theory of operation.

I have a service ticket open with Tesla. Fear something is amiss which prompted the “replace 12v battery soon” message On my prior AGM battery.

 

[murphyS90D]

Full charge on a 12 volt battery is 12.7 volts. Anything higher than that means that it is being charged. I don't have my chart handy but my memory says that 50% charge is 12.2 volts. As the battery ages the charge cycles occur more often. When my 2016 was new it was 3 times in 24 hours if the car wasn't driven. Today 5 years later it is 6 times in 24 hours. The CCA has dropped from 600 to 180. I have not seen a 12 volt battery warning. An Ohmmu battery should be delivered today. Unfortunately the car is stuck in service for the radio upgrade. The first radio they received was DOA. Hopefuly the second one will be installed on Monday and will work.

 

[N4HHE]

12.6 is full charge on an AGM battery but it takes 13.6 or more to get to the full charge. After charging there is a capacitive ”surface charge” that has to be burned off to measure voltage if the core charge. This is why one runs the headlights engine off to get an accurate voltage measure of SOC. But my 13.5-14.14-13.5 infinite loop just isn‘t right.

Since getting the car to sleep I have not caught it in this 12v charging loop. However when the car is awake but not fully booted to run, I hear a whine in the frunk. Power steering?

Appointment in Brentwood 5/25.

 

[John in LB]

The 12v battery life is not very long. If you don't get to drive your Tesla much due to travel or if you park for long periods of time for work trips or vacations or If you own and drive other vehicles and your tesla sits then the 12v battery will die in 7 months to a year. The less you drive it the faster your 12v battery will die. There are a few strings here that owners mention replacing the battery every other year. I did this to extend the life of the 12v since I travel a lot and the car sits. Even with daily use the car drains the 12v battery using all the many features such as the door handles opening and closing, the mirrors opening and closing, the computer communicating to wifi or your cell phone, etc. Many have experienced the 12v battery die and they needed to jump start the battery. Others receive a warning message about the 12v battery but after the warning there is no indication of how much time you have remaining until total loss of power and once its out then nothing will function. It was a low price modification that cost under $90. It was $65 for the 12v 5amp battery tender, $12.38 for the sidewall port connector, and $10.99 for the 6ft terminal cable. My first 12v battery replacement was free under warranty, however the next one will not be covered under warranty. The 12v batteries are very expensive and only available through Tesla based on size and terminal port configuration. Others have did trial and error using other type battery brands and sizes but they didn't fit or had other issues trying to screw the Tesla battery terminals in to the non tesla battery. My project is simply an experiment to see if I can extend the battery life longer than relying on the regenerative features of letting the vehicle charge the battery while driving. Many others on TMC Forum are doing this and its working. This is just another way that I am sharing.

Well? It's been about 18 months since you installed a battery maintainer... any comments or hints as to battery life? Is it lasting longer, or did you still end up with a failed battery after a couple of years? Let me know... thanks.

 

[John in LB]

I tried three different sized battery tenders (2 amps, 3 amps and 5 amps.) The last one was a BATTERY TENDER, model 022-0186G-DL-WH, rated for a maximum output of 60 watts (5 amps).

I am giving up on the idea of using a battery tender on my 2017 Model X. The primary problem is that the Tesla keeps running electronics and draws more than 60 watts. Over 24 hours, the Tender kept trying to charge and actually got warm. It never went into a trickle mode.

I appreciate that the 12V battery gets charged via the HV battery. I have watched the charging relay open / close - so, I know it is a bit harsher as compared to a trickle charger. As I store the car for several months a year, I was hoping to extend the life of my 12V battery - last one lasted under 3 years.

Bottom line, I don't feel comfortable using the battery tender unattended for several months (when the car is in storage.)

 

[murphyS90D]

Use a full size smart battery charger. They cost more than $100. I use one made by Schumacher. I got it from Amazon.

 

[John in LB]

I don't think a higher rated charger would provide any benefit. Might as well let the on board charger manage the whole thing...