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Main battery voltage too low, will not charge

k0s0vo

Member
Feb 21, 2020
10
3
UK
Moderation comment - thread moved from UK and Ireland sub forum for greater visibility

I bought this Tesla Model S 85 few months back. Was scraped on the left hand side, no airbags deployed, no error messages.

I drove it home and charged fine. Took it at the end of September to a body shop for repair. They were quite busy and the car sat for ages. About 10 days ago they called and said they need to move the car but shows 0 miles and will not drive.

I ordered a 3 pin plug charger and went there. Started to charge fine. Probably they only left it for few miles range. Called me again days later that it shows again 0 miles, and will not start. The charge port will not open. We had a fully charge 12v battery connected to the car. Opened manually the charge port, also had to unlock it manually from inside the trunk, plugged in the charger, says starting to charge, but few seconds after said charging complete, but still 0 miles. Took it home on a recovery truck
Tried with my home wall charger but same results.
I'm guessing the main battery voltage is too low. How do I put some volts in?
 

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tsh2

Member
Aug 27, 2019
317
95
Cambridge, UK
The 12V battery is probably dead again, unless you have a new replacement. Lead Acids really don't like to be discharged.

Leave it plugged in, it may slowly recharge the pack and start working after a day or so - or maybe it is shut off for safety. Look in the main forum under battery, this is not a UK specific problem.
 

Adopado

Active Member
Aug 19, 2019
4,950
3,763
Scotland
Complete guess here, but is it possible if the battery pack is totally empty there is not enough power to engage the main breaker (assuming that the system that engages it cant be powered from the 12v/charge port connection)

There's a video on Youtube of James May who had this issue for similar reasons with his Model S... he made an addition to help deal with any future instance ... but I'm sure OP and he will manage to avoid that now that you know!
 
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Reactions: Alistairuk

k0s0vo

Member
Feb 21, 2020
10
3
UK
Looked a lot online and couldn't find anything. Send same message to Electrified Garage USA, just got this response, see screenshot attached.
12v 110amp battery is on charge overnight and I have 120amps boost charger. Will give it a try tomorrow. Fingers crossed
 

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tsh2

Member
Aug 27, 2019
317
95
Cambridge, UK
Good to know. Tangentially, I saw that the newest cars have a lithium '12V' pack, and these have a surprisingly large supply current capability in relation to their charge capacity. (I think stepped up from 3 cells). I expect the monitoring circuits will want to see that the 12V rail holds up under heavy load since the sign of any battery being tired is that the internal resistance increases (off load voltage looks OK, on load is poor).
 

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