Brass Guy
Active Member
My 2013 has had the 12V replaced twice, the second time was this year; so just about 4 years each.
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Any reason not to hook up a battery tender to the 12 volt battery ?
- Thread starter edgrzy
- Start date
I am also still on original battery, a MS 100D 2017, 60K miles. Not complaining!
Watts_Up
Well-Known Member
Are you sure about this?
I don't have a Model S but a Model 3, and I installed a Bluetooth 12 V monitor.
I have on my phone a recording graph showing that when the car is sleeping,
the inboard DC/DC converter re-charges the 12 V battery for 2 hours about every 2 days.
Basically, charging is performed at 14.5 V. After charging the battery voltage is around 13.5 V
When the battery reach 12.5 V the DC/DC converter get triggered.
Page 22 in the manual:
Note: Power is available whenever the vehicle is considered "awake" The vehicle may be awake for many reasons. For example, when using features such as Summon, or when features such as Cabin Overheat Protection, Keep Climate On, Dog Mode, Sentry Mode, etc. are enabled. The vehicle is also awake whenever the 12V battery is being charged or is in use, during HV charging, when the vehicle is communicating with the mobile app, etc. Leaving an accessory plugged in does not deplete the 12V battery.
So technically it's when you're driving or it's driving lol.
whitex
Well-Known Member
The above just means the vehicle wakes up whenever 12V needs a charge. The vehicle does not need to be driven or have anyone in it to be awake.
12V battery automatically charges whenever needed, whether you are parked or driving. Without that, the 12V battery could drain in a matter of hours. It would not last overnight if the battery cooling pumps need to run because it's too hot or too cold outside. When I physically removed my MCU for fix the emmc chip, the 12V battery drained in about 3 hours because the MCU could not initiate 12V charging (engages the HV battery and DC-DC converter).
You can hear your contactors turning on whenever 12V is beginning to charge. Record your Tesla sounds overnight, you will hear how many times it kicked in.
Last edited:
How many times?
When the HV is connected the car is "on", that's what I meant by driving.
whitex
Well-Known Member
Once for each time the car starts using the HV battery, and once when it stops.
Well, by that definition then your Tesla is "driving" multiple times a day, all by itself even while you sleep and the car is in the garage. Hmmm.... I think I see where you're going with this, you can now claim that Full Self Driving is fully functional, since "drives" completely by itself without any human supervision. As an added bonus, all Tesla's now have this your definition FSD, even 2012 Teslas without any autopilot hardware? Is that you Elon? Laying the ground work for why FSD is done and you owe nothing more to anyone who paid for it?
I also have a Bluetooth monitor on my Model 3 but my time between top offs is 17hrs+/- and the time awake charging is 2+hrs (maybe something changed hardware wise between our cars?). When I purchased the battery monitor a few years ago, anytime the car was awaken it stayed awake for at least 4 hours normally 6 hours. After Tesla replaced the 12V battery along with my PCS board last August, I thought the time between top offs and charging time would change, it did not. Two years back I connected a Smart Charger to try and keep the car from staying awake for so long but it still woke up for 4 to 6 hours, even though the battery post voltage was over 13V. Since the charging regime has changed, maybe I should perform my tests again? Last time I measure the 12V power usage during sleep state it was 6 or 7 watts, it's the awake power usage (around 250W) that adds up.
Since my Smart Charger is capable of delivering way more than 7W, the car should not need to wake up ever to top off the 12V battery but I know it does wake up for other reasons. As I remember. my Smart Charger averaged around 10W from the AC wall outlet while maintaining the float voltage (that would be around 240W/day. My daily power usage while parked is close to 1KW.
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