What happens when a HV battery gets REALLY dead

[jeluthadamaja]

I know it is bad to run the battery down to nothing, but when the car BMS is working well I assume that is basically impossible to do without really trying.

Unfortunately I'm dealing with a fried MCU, which lets the car work in a very limited state. Its been over 3 weeks, and when Tesla initially diagnosed it about 2 weeks ago the charging functions worked, but since then car has since refused to charge. I wasn't that worried about it since I wasn't driving it, but the vampire drain now has my car at 10 miles of range with another 2 full days before Tesla installs the new part. I'm worried that by then, the car battery will be fully depleted...

On another note, not having Service Centers in New Mexico due to archaic laws in the state is a brutal situation for Tesla owners. I love my cars but it is kind of ridiculous that it takes a month to replace a computer that essentially just plugs in... I would have loved to have done this replacement myself, mainly just to save on the time my car has been out of service. (Don't get me started on the ridiculous out-of-warrant cost...~$2000+.... I'm hoping they goodwill the part)

 

[Tam]

...I'm worried that by then, the car battery will be fully depleted...

The manual says:

"Discharging the Battery to 0% may permanently damage the Battery. To protect against a complete discharge, Model S enters a low-power consumption mode when the charge level drops to 5%. In this mode, the Battery stops supporting the onboard electronics to slow the discharge rate to approximately 4% per month. Once this low power consumption mode is active, it is important to plug in Model S within two months to avoid Battery damage. Note: When the low-power consumption mode is active, the auxiliary 12V battery is no longer being charged and can completely discharge within 12 hours. In the unlikely event that this occurs, you may need to jump start or replace the 12V battery before you can charge. In this situation, contact Tesla."

Your main battery will protect itself so I don't worry about it but your 12V will definitely be depleted so I would start get an external 12V charger and trickle charge it.

 

[jeluthadamaja]

The manual says:

"Discharging the Battery to 0% may permanently damage the Battery. To protect against a complete discharge, Model S enters a low-power consumption mode when the charge level drops to 5%. In this mode, the Battery stops supporting the onboard electronics to slow the discharge rate to approximately 4% per month. Once this low power consumption mode is active, it is important to plug in Model S within two months to avoid Battery damage. Note: When the low-power consumption mode is active, the auxiliary 12V battery is no longer being charged and can completely discharge within 12 hours. In the unlikely event that this occurs, you may need to jump start or replace the 12V battery before you can charge. In this situation, contact Tesla."

Your main battery will protect itself so I don't worry about it but your 12V will definitely be depleted so I would start get an external 12V charger and trickle charge it.

Thanks... I remember seeing this, but forgot about it until now. I hope whatever system is telling the battery to go into 'low power consumption' mode is still operating... I think it is, but the car is far from fully functional.

 

[ewoodrick]

You should be fine. It’s not an uncommon situation, auction cars have this happen a lot.

BUT, you really shouldn’t know the current status, because you should be letting the car stay asleep, even turning off remote access

 

[TMeister]

Your main battery will protect itself so I don't worry about it but your 12V will definitely be depleted so I would start get an external 12V charger and trickle charge it.

Knowing that you can no longer charge the main battery makes this advice very important. Put the 12v system on a trickle charger and the HV battery will no longer experience vampire drain (other than internal loss) powering the 12v system.

 

[jeluthadamaja]

You should be fine. It’s not an uncommon situation, auction cars have this happen a lot.

BUT, you really shouldn’t know the current status, because you should be letting the car stay asleep, even turning off remote access

I totally agree with you... I've only checked it about 3 times since I noticed it stopped taking a charge, but recognize that everytime I check it wakes up and drains more. The car seems to be going into a deep sleep, since everytime I've checked it the dashboard screen reboots before it shows the charge status. Remote access hasn't worked at all, and the main 17" screen is completely blank.

Thanks for everyones input. I'll put a trickle charge on the 12V battery tonight

 

[JoeMartin]

Also, I'm surprised you've lost all charging capability. When my MCU fully died I was able to charge about 1 KWh/8 hours. Definitely not something that would make the car able to be driven, but enough that it would keep the car from depleting.