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Weird issue with 12V Battery

goodbadboys9

Member
Apr 22, 2018
100
23
NJ
I replaced Intelligent Sensor & I still have the issue. Does anyone know what would be the float rate for 12V battery when not charged by DC-DC converter?
 

JoeS

Member
Jan 28, 2016
36
22
Hills Above Silicon Valley
Whenever the car is ON the dc-dc converter charges the 12v battery at 14.4v, at room ambient temperatures. Trouble is, as soon as the car turns OFF, its vampire load is significant (I measure 1.25A on my 2013MS85) and pulls down the 12v battery, easily below 12.5vdc. Without any load, the AGM battery would otherwise stabilize around 12.8v. The battery specs say that the ideal float voltage is 13.7v at room ambient. To avoid the car waking up and recharging the 12v battery, I keep a continuous float charger on my 12v battery whenever the car is in the garage. The vampire load used to be ~04A for a few years, but, seemingly after some software updates last year, it now runs a around 1.25A, despite Display Energy Save mode being ON and Always Connected being unchecked.
 

goodbadboys9

Member
Apr 22, 2018
100
23
NJ
Whenever the car is ON the dc-dc converter charges the 12v battery at 14.4v, at room ambient temperatures. Trouble is, as soon as the car turns OFF, its vampire load is significant (I measure 1.25A on my 2013MS85) and pulls down the 12v battery, easily below 12.5vdc. Without any load, the AGM battery would otherwise stabilize around 12.8v. The battery specs say that the ideal float voltage is 13.7v at room ambient. To avoid the car waking up and recharging the 12v battery, I keep a continuous float charger on my 12v battery whenever the car is in the garage. The vampire load used to be ~04A for a few years, but, seemingly after some software updates last year, it now runs a around 1.25A, despite Display Energy Save mode being ON and Always Connected being unchecked.

This is similar to my problem & whenever battery comes down to 12.5V do you get any error messages saying car cant start & need service etc?
How do you keep float charge ~13V.I am assuming you are using battery tenderizer?
 

wycolo

Active Member
May 16, 2012
3,092
428
WA & WY
The old cars don't have a convenient connection for a 12v Tenderizer afaik since the cigar outlets die when car turns off. The cable chargers should have had a built-in Tenderizer from day one considering all the abuse that this poor lead-acid suffers. My 2012 MS currently has this same problem but totally kills the 12v battery.
--
 

goodbadboys9

Member
Apr 22, 2018
100
23
NJ
The old cars don't have a convenient connection for a 12v Tenderizer afaik since the cigar outlets die when car turns off. The cable chargers should have had a built-in Tenderizer from day one considering all the abuse that this poor lead-acid suffers. My 2012 MS currently has this same problem but totally kills the 12v battery.
--

If the battery comes down below 12.5V.Does it give you any errors?
I assume DC-D Converter should run more frequently to keep the battery charged to maintain >13V
 

cab

Active Member
Sep 5, 2013
1,033
721
Grapevine, TX
Any update on this?

My car (a 2013) threw these same messages the other day. The battery was at 11.6 or so volts. I put it on my 12V charger and it charged up fine and the error messages went away. I was able to drive it to the service center and now, a couple days later they are indicating it is the DC to DC converter. The tech has indicated an "internal switch is faulting" and there are voltage spikes and drops. Of course since actually TALKING to someone at Tesla is all but impossible (over the phone) I am stuck exchanging text messages in 2 hour intervals. In short, no pun intended, I'm not sure if this is something they actually measured OR if they are just inferring that it "must be the DC to DC converter".

I didn't think to check the heater or A/C on the drive to the service center, but I THINK the former was working (it was a mild day though) - aka, I didn't do a check that might have told me if the fuses in the DC?DC converter were blown.

At this point, I have told them to pack it up and I'll come get it. I'm just not quite convinced the DC/DC is bad...at least not $3K convinced (note: apparently that cost includes a retrofit to the gen 2 unit...nice, but sheesh!) on New Year's Eve!
 

goodbadboys9

Member
Apr 22, 2018
100
23
NJ
No updates yet. Sorry for your pain .I am kind of surprised with all of the sensors in the car they cant nail down exact issue. Couple of repairs like these will change optics of EV car
 

JoeS

Member
Jan 28, 2016
36
22
Hills Above Silicon Valley
cab, sorry to hear. If it were the dc-dc then when you turn the car on (just by entering it) I would expect the 12v battery voltage to keep dropping as the car's active 12v load would be greater. If the battery voltage goes up, then there is perhaps a different problem? My MS85 is used exclusively for long trips and the rest of the time it sits in the garage with the cover on and the 12v battery on a charger. I replaced the Battery Tender(izer);) with a small Meanwell power supply set to the AGM battery manufacturer's recommended 3.7vdc. For months it's now settled down to a 'vampire' 1.21A draw at 13.7v. I attached a two-prong SAE connector through a fuse to the power and ground terminals behind the nosecone and brought the wire for the charger up through the hole for the hood latch, taped it down flat, and leave it tucked under the rubber hood seal when not in use. Since I always am either using the car or have it parked with the charger attached I haven't experienced the battery voltage drop down to 12.5v.
 
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