12 volt battery dead

[apacheguy]

Tesla did their usual fine job. The 12v problem was unrelated to the charger problem. Many of you may know, but I did not, that the entire electrical support of our cars comes from the 12v. That include the charging status monitoring system, which also includes the connecter release process. No 12v and the cannot know if the charging session has ended nor an it then release a connector. Thus, jump the 12v and everything will cycle on after a few minutes, as it did in mine.

As as the more knowledgable people here keep saying, no long term solution until Tesla redesigns the system to reduce the loads on the 12v and/or remove as much as possible from the 12v system. I now understand that this is quite a dilemma for a low volume manufacturer like Tesla because sourcing 12v high quality cheap parts us easy, sourcing anything else is expensive, slow and often lower quality. Hopefully Model X has improvement in this respect. I'll wager the only short term solution for Tesla is probably more robust 12v batteries.

Can you clarify exactly what the problem was? On your repair order it only lists a 12 V replacement? Nothing else?

 

[Cottonwood]

One of the biggest ongoing complaints in the Prius group is the 12V battery dying. I don't know how common it is now, but many Leaf owners put a quick disconnect switch on their 12V battery, which doesn't charge while the car is plugged in. So if Toyota and Nissan can't get it right...

Of course, if a larger battery was used, it wouldn't cycle nearly as often and the problem would be minimized.

The reason for the death of Prius 12V batteries is very different from MS 12V battery death. The Prius Vampire load is measured in 10's of milliAmps, while the MS Vampire load is measured in Amps. That means that the Prius has a Vampire load that is about 100 times less than the MS. On the other hand, the Prius only tops up its 12V battery while running, not while in the off state. That means that the Prius, if not started for several weeks, will draw the 12V to a VERY low state of charge, 100% discharge.

While a good deep cycle 12V battery may be good for 500-1000 equivalent charge cycles (that is how an MS kills its 12V battery), it only takes a few 100% discharges to kill a 12V battery. Leave a Prius 3-6 weeks without starting, several times and the battery dies.

That is why a Prius 12V battery with a tiny maintainer (10's of mA) will last a very long time, but it takes a much larger charger (4-10 Amps) to keep an MS 12V battery happy.

 

[martinwinlow]

The Mitsubishi i-MiEV is the same - only worse. I fitted an OVMS to mine which draws about 50mA on top of whatever the normal vampire draw is and if I don't start it within a week it won't start and I have to jump start it. This is with even a brand new battery (the old one would go flat in a day). I would really like to modify the charging input so that once charging has finished, rather than sit there doing nothing, I could use the mains supply to power a cabin pre-heater in winter and a battery conditioner all the time. Interestingly, I see that the MS' auxiliary battery is the same size as my i-MiEV's at about 35Ah! MW