Mine died with no warning, leaving my wife stranded. Then Tesla would change it under warranty, but they wanted to tow it. So, more waiting and then a drive the next day to pickup the car.
With an ICE car, the car does not tell you when to replace 12v battery. I normally replace 12v batteries around the 4-5 year intervals in my ICE cars. Sooner if I have some travel plans and doing some prep maintenance.
Tesla have changed the way they charge and monitor the 12v battery for the better through software updates. As far as actual physical changes to the 12v battery, it's arguable as to whether they've made any improvements. There have only been 2 revisions on the 12v battery, with part number 1129182-00-A being used for Model 3 up to around April 2018. The newer revision with part number 1129182-00-B had been used ever since, up until the newest OEM lithium ion low voltage battery. We don't know what exactly changed between the revisions A and B, and if it was for better qualities or for cost reduction. However, my Model 3 was made in March 2018 and has the revision A battery which is still working fine after almost 4 years and 73,200 miles.
Be interesting to see changes quantified I.e. batteries will now last x% longer.
Honestly I don't think they improved the capacity of the batteries, since they have the same Ah rating. Most likely they made changes to how they are made in order to mass produce them quicker, or more cheaply. The beginning of 2018 was when Tesla was just starting to ramp up production of the Model 3 and they were going through production hell. So my guess is that they allowed changes in order for the manufacturer (Hankook/AtlasBX) to be able to meet demand for them or to save money on them.
the difference is that with an ICE car (in my 45 yrs of experience with over a dozen of them), when an ICE 12V battery dies, it has never been "catastrophic" (dead is dead). I have never been locked out of the car. I could always get it jump started and be on my way -- never stranded. I could take my time, sometimes more than a week, to figure out how best to get it replaced. Maybe I'd have to drive around with a portable jump starter, but otherwise no big deal.
If you want as similar an experience you can get, you can leave a jump starter in the frunk and then hide a battery that can pop the frunk somewhere (so you can use it on the leads in the tow hook cover). If the 12V is completely dead, the frunk should be able to pop (the only situation where this might not work is if the 12V still has enough charge to keep frunk locked, but not enough to unlock car).
FWIW, that’s one tech with his small sample. That tech may also be new. Earlier versions of the firmware did not even have a warning message so 12v failure em was ALWAYS unannounced. Now there are warnings, but it is my impression anecdotally through forum that they have a short leash (do it NOW). There are also still catastrophic unannounced 12v failures… a friend of mine had one several months ago. It was in an ‘18 3, and tech told them that early batteries had a flaw… so if you have an old 3, replace your battery! Both of mine are ‘18 and i’m having both 4 year old batteries replaced next week via mobile service. $100 is a small price to pay every few years to avoid being stranded.
My point really wasn't pertaining to proactive swapping of the lead acid battery it was more directed at getting the lithium battery.
Several have reported that they got a warning and then it died soon after. Most get no warning.
