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12v battery replacement - data, surprise

drg_mx

Member
Dec 20, 2018
30
4
morris, nj
car 2017 mx, 90d 29k miles, true age 4yr + 4 months

a few days back (call it day 0o) got the unavoidable- *12 V battery needs replacement soon

the first question that popped up : what does *soon* mean? could not reach tesla, the forums articles indicated 1 wk to a couple of months.

drove to tesla the next day, they agreed to send a rover in 3 days, they did, and the battery was replaced on 4th day after the warning ( call it day 0n)

also many articles indicated the battery "stage of charge" vs voltage: about 50 to 70% at 12.5 volts, so to estimate how bad ny battery was, i took many measurements....

a. replacement surprise:

all the posts/videos i read/saw indicated that tesla needs to reset the warning with a computer after installation.

my experience-- not so...the tech went straight to the frunk ( no shutting off power) and replaced the battery. then he opened the driverside door, the warnig was gone, both screens powered up,,,no resetting or further action was needed.

b...voltage data old battery: (would like to see others measurements)
0o + 4 hrs 13.4 (assuming charging in progress
0o+12 hrs 12.5
then all measurements were between 12.4 and 12.6 with car charger plugged and unplugged for hors.

data new battery
0n 14.4
0n + 12 hrs (charger plugged in) 13.3

after that all reading in the next three days were between 13.3 and 13.4, weather the charger was plugged in or not.

i am sure i will not have to go thru with this again but will love to see measurements from others.
 

peety3

Member
Jan 29, 2021
64
30
Duvall, WA
Voltage is not the ideal measurement of battery state and/or performance. Current tracking (via a low-resistance shut that in turn is voltage-delta monitored) is best. There's also a question of whether the DC-DC converter was passing electrons from the HV battery to the 12V battery at the time(s) you were doing your measurements.
 

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