I am wondering whether the new lithium 12v battery in Plaid will fit M3 or MY

[Phlier]

It's absolutely not worth switching out the lead acid in the Model 3 for a lithium ion battery, IMO.

Here in the desert, the summer sun just destroys traditional lead-acid car batteries. In the car that we leave outside all year long, I'm very lucky to get two years out of a battery. The norm is about 18 months.

To the OP... It depends on how Tesla implements the new 12v lithium battery. If the battery itself has an onboard BMS system, and can handle the charging logic used to charge a 12v lead-acid battery, then it would most likely be OK. But if the 12v battery charging logic is handled by the car's computer, it wouldn't be OK, as our Model 3's don't have the capability to charge anything other than the OEM 12v lead-acid battery.

The currently available after market Lithium Iron Phosphate (or Lithium Ferrous Phosphate, if you prefer) batteries have their own onboard BMS system that deals with whatever voltage and current it gets (within reason), and distributes it to the battery cells appropriately. So these will work even in Model 3's, where the car thinks that it is charging a traditional lead-acid battery.

TL;DR If the new Tesla 12v lithium battery has its own BMS system and can handle lead-acid charging logic, it might work. If it does not have its own BMS, no, it won't work.

 

[Let's Drive]

Lithium batteries for cars and motorcycles are absolute crap in winter; that's just the way they are. Unless it's a special unit, with special chemistry, I rather keep the 51R. People I know with those on motorcycles, they don't crank in about 50F. You need to turn headlights on for about 5 minues, so they 'heat' enough to be able to crank the engine. And if the headlights don't turn on unless engine is running, well, you'd be screwed.

Hmm, that's not been my experience. I've ran a Braille GU1R in my other car since 2013, and it's spent many nights parked in winter freezing temps, only to start the car just fine.

In fact, I got so used to it starting reliably, Covid ended up doing it in, as I didn't drive the car enough.