High Drain from HV Battery after 12V Replacement?

[cowleggies]

Hi all,
Asking this mostly out of curiosity as I think I know the answer - I had my 12V battery replaced this morning, drove to work immediately afterwards, and parked. I happened to glance at my Tesla widget on my phone around lunch and noticed that my HV battery had drained ~10% since parking this morning, which is obviously not normal behavior. In the last two hours, the drain has stopped and it's back to expected idle behavior.

I know that the 12V battery is charged off of the HV battery with the onboard DC-DC converter and the tech mentioned that it's not uncommon for their 12V battery stock to sit around in the SC or in Ranger vehicles for an extended period of time, so occasionally when they replace a 12V with a "new" battery they are drained or even completely dead. - am I safe to assume the drain from the HV battery was just getting the new 12V properly charged? Anyone else see this behavior after a 12V replacement?

 

[GtiMart]

When installing a 12V battery in an ICE car, the 12V should be fully charged before installation. On a Tesla, as they know the HV will charge it, maybe they are more "loose". With that said, 10% of your battery is between 6-8kWh depending on your model. That's a lot of energy, I'm not sure all of that fits in a 12V... Even if you count the loss of running the car's computer and pumps during the charge, it's still high... I don't have a proper explanation,

With that said, if it did it once and it behaves correctly after that, their explanation could be correct.

 

[cowleggies]

When installing a 12V battery in an ICE car, the 12V should be fully charged before installation. On a Tesla, as they know the HV will charge it, maybe they are more "loose". With that said, 10% of your battery is between 6-8kWh depending on your model. That's a lot of energy, I'm not sure all of that fits in a 12V... Even if you count the loss of running the car's computer and pumps during the charge, it's still high... I don't have a proper explanation,

With that said, if it did it once and it behaves correctly after that, their explanation could be correct.

Thanks for your insight. I think there may be some BMS calibration at play here too as the SoC jumped up by 4-5% from where it was when I arrived at the SC and when I left - so the actual loss may be less than that. Tessie shows about 4 kW drained since I parked this morning.

I’ll chalk it up to strangeness around the 12V being replaced unless it happens again - this is the first time I’ve ever seen drain like that (and hopefully the last!)

 

[AlanSubie4Life]

That's a lot of energy, I'm not sure all of that fits in a 12V

I think it is something like 500Wh. The most I have seen ever drawn is something on the order of 300Wh (7W for 40 hours). Just roughly.

What is being observed is just BMS adjustments.

Lots of reports of bizarre behavior - check the energy screen to see it jumping up and down by huge increments.

No idea if this is a bug or whether it has always been happening and is more observable now. I remember years ago I have seen 10-mile jumps but they didn’t seem that common - but hard to say.

I fairly routinely lose 8 miles after every charge session to ~60%. Sometimes it comes back after a drive.