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KArnold

Active Member
May 21, 2017
1,803
1,998
Columbus OH
I just returned from a 3-week trip to Uganda. My 7-month old MS100D sat idle during that time plugged into my garage Nema 14-50, in the garage, with max SOC set to 75%. Ambient temps were 20's and 30's.

Upon return I'm getting the "12v Battery needs service, replace". Email' d the local SC to see if they will send a Ranger.

I assume this would be covered by warranty? And I assume the lack of driving is related? I've heard of 12v's needing replacement at a year, but 7 months? If normal that sounds like a design problem.
 
Sorry for your troubles.

While inconvenient, I’m sure you realize 12V batteries fail in ICE cars regularly. In fact, I seem to replace them in my ICE cars every 2-3 years now for decades.

7 months is quite early, however it happens and perhaps you just got a bad 12V battery. Who knows?

“Design flaw.” Doubtful. That’s like blaming Tesla when a tire goes flat, or a wiper blade starts chattering.
 
“Design flaw.” Doubtful. That’s like blaming Tesla when a tire goes flat, or a wiper blade starts chattering.

Thanks for your response.

First of all, I admit than other than my experience in an ICE vehicle, I've know little about batteries. That's why I'm seeking the collective knowledge and experience.

Another thread quoted Syonyk's Project Blog: Tesla Model S 12V Battery Analysis. In that article the author says about the 12-volt battery (among other things)
I'm not convinced that the charge time per cycle is enough. The initial charge current is fine, and the taper off is normal, but I'm not convinced that this battery is ever really 100% charged. Being fully charged on a regular basis is essential to prevent sulfation of the negative plate, and it helps balance charge between positive and negative plates as well.
If true, I would consider that to be a potential design flaw.

I'm less concerned about design issues but would like to know what I can to to help, if anything. I'm about to have a new 12-volt battery installed by Tesla. If connecting that 12-volt to a smart, trickle charger (a.k.a. Battery Tender or similar) nightly would increase the normal life of my 12-volt battery from 1 year to 3 years, that is well worth my effort. I guess that is really what I'm asking.

I don't even know if a smart charger is designed to work with lead acid batteries, so this may be a futile effort anyway.

Also, my 12-volt message (again, 7-month old 2017) started after being parked, but plugged in, for 3 weeks. I'd also like to know if "driving" (as opposed to being plugged in) affects the 12-volt charge cycle at all. Again, if so, maybe a trickle charger makes sense in those situations.

Thank you again.
 
Thanks for your response.

First of all, I admit than other than my experience in an ICE vehicle, I've know little about batteries. That's why I'm seeking the collective knowledge and experience.

Another thread quoted Syonyk's Project Blog: Tesla Model S 12V Battery Analysis. In that article the author says about the 12-volt battery (among other things) If true, I would consider that to be a potential design flaw.

I'm less concerned about design issues but would like to know what I can to to help, if anything. I'm about to have a new 12-volt battery installed by Tesla. If connecting that 12-volt to a smart, trickle charger (a.k.a. Battery Tender or similar) nightly would increase the normal life of my 12-volt battery from 1 year to 3 years, that is well worth my effort. I guess that is really what I'm asking.

I don't even know if a smart charger is designed to work with lead acid batteries, so this may be a futile effort anyway.

Also, my 12-volt message (again, 7-month old 2017) started after being parked, but plugged in, for 3 weeks. I'd also like to know if "driving" (as opposed to being plugged in) affects the 12-volt charge cycle at all. Again, if so, maybe a trickle charger makes sense in those situations.

Thank you again.
These are very good questions, and there are some good answers to them.

1)Yes, everything will be covered by initial warranty for the 4 years 50K miles, so this included.

There are two modes about the Tesla 12V. When the car is on, the main battery pack is connected, and it's using a DC to DC voltage converter circuit to keep the 12V battery full basically all the time. The 12V would basically never get drained, and that's about the healthiest thing for a lead acid battery. If you were driving your car round the clock with it on all the time, the 12V battery would probably last many years.

The other mode is when it is off. For safety, the car isolates the high voltage battery pack, and the 12V battery is on its own to run all the idle standby electronics. This is higher use than most gas cars when they are off, and the Tesla 12V is fairly small capacity, so it will drain it down in several hours. When it detects that it is low, it will re-engage the main battery and fill the 12V back up and then disengages again. That cycle of depleting and refilling the 12V will happen somewhere around maybe 3-4 times a day when the car is not on and being driven, even when the charging cable is plugged into it.

So that kind of use is pretty hard on the lead acid 12V batteries, running through a lot of cycles.

So now to your other question--yes, you can put a battery tender on it when it's parked, and that will supply the energy for all of those 12V electronics loads and not continually empty and refill that battery, thus wearing it out quickly. And yes, that will dramatically extend the life of that battery by never letting it get low. Here is a forum thread about someone doing that with an external battery tender device like that.
Any reason not to hook up a battery tender to the 12 volt battery ?
 
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