MISSION - I want to be proactive with regard to my 12v battery without being paranoid and replacing the 12v battery every 3 years. I am happy to "test" it every 6 months and recording the readings. Then replace the 12v battery when it shows signs of old age.
OVERVIEW - I charge my 2020 i3S every 3-4 days. It has 40K miles. The 12v battery is probably 5 years old as I have had the car since Aug 2020. NOTE: My former 2014 i3 REX and it's 12v battery was at 60K miles and 6 years old when I traded it in for my i3S.
PROPOSED TEST PROCEDURE
1. I believe that testing the "no-load" voltage (also know as "Open Circuit Voltage test - OCV) will be somewhat useful in showing the condition of the 12v battery. But a recently charged battery may hold a residual charge, giving a false high reading. To get an accurate OCV, I understand you let the battery sit for at least 12 hours after charging then measure it with a multimeter. I hope that information is accurate for a AGM battery. From a source on the Internet:
a. 12.6v - 12.8v = fully charged
b. 12.4v - 12.6v = 75% charged
c. 12.1v - 12.4 = 50% charged
2. From what I have read, the 12v plug (cigarette lighter) in the center console will provide the non-load value of the 12 v battery after the car goes "dormant" (as long as the fuse hasn't blown.)
3. How does this sound for a test procedure based on items 1. and 2. above: WARNING- Don't do this until this test has been properly vetted!!!!!! (i.e. people who know what they are doing)
A. Fully charge your high voltage battery (Day 1 of test)
B. Make a ~6 foot-long electrical cord that has a cigarette plug on one end and properly insulated connectors on the other end so that you can test the 12v battery voltage. WARNING - make sure that you do not have any exposed contacts. You need to avoid shorting anything!
C. Label the connectors on the electrical cord with the verified "+" and "-" polarity.
D. Make this test so you can test the 12v outlet without opening the car door (i.e. roll down a window)
E. (Day 2+) Do not plug in your i3 high voltage charging cord during this test and do not open any door.
F. Install the electrical cord into the cigarette plug in the center console.
G. With the electrical test cord through the open window, close door but don't lock the car (i think that turns on the alarm causing voltage drain and possible alarm from movement in the car.
H. Wait ________ minutes until the i3 _________ circuit goes dormant.
I. Set multimeter to measure DC voltage at the scale appropriate for 12 volts
J. Insert multimeter probes into correct "+" and "-" connectors
K. Write down the date, time since disconnecting the last time you charged your high voltage battery, and of course write down the 12v battery voltage.
OVERVIEW - I charge my 2020 i3S every 3-4 days. It has 40K miles. The 12v battery is probably 5 years old as I have had the car since Aug 2020. NOTE: My former 2014 i3 REX and it's 12v battery was at 60K miles and 6 years old when I traded it in for my i3S.
PROPOSED TEST PROCEDURE
1. I believe that testing the "no-load" voltage (also know as "Open Circuit Voltage test - OCV) will be somewhat useful in showing the condition of the 12v battery. But a recently charged battery may hold a residual charge, giving a false high reading. To get an accurate OCV, I understand you let the battery sit for at least 12 hours after charging then measure it with a multimeter. I hope that information is accurate for a AGM battery. From a source on the Internet:
a. 12.6v - 12.8v = fully charged
b. 12.4v - 12.6v = 75% charged
c. 12.1v - 12.4 = 50% charged
2. From what I have read, the 12v plug (cigarette lighter) in the center console will provide the non-load value of the 12 v battery after the car goes "dormant" (as long as the fuse hasn't blown.)
3. How does this sound for a test procedure based on items 1. and 2. above: WARNING- Don't do this until this test has been properly vetted!!!!!! (i.e. people who know what they are doing)
A. Fully charge your high voltage battery (Day 1 of test)
B. Make a ~6 foot-long electrical cord that has a cigarette plug on one end and properly insulated connectors on the other end so that you can test the 12v battery voltage. WARNING - make sure that you do not have any exposed contacts. You need to avoid shorting anything!
C. Label the connectors on the electrical cord with the verified "+" and "-" polarity.
D. Make this test so you can test the 12v outlet without opening the car door (i.e. roll down a window)
E. (Day 2+) Do not plug in your i3 high voltage charging cord during this test and do not open any door.
F. Install the electrical cord into the cigarette plug in the center console.
G. With the electrical test cord through the open window, close door but don't lock the car (i think that turns on the alarm causing voltage drain and possible alarm from movement in the car.
H. Wait ________ minutes until the i3 _________ circuit goes dormant.
I. Set multimeter to measure DC voltage at the scale appropriate for 12 volts
J. Insert multimeter probes into correct "+" and "-" connectors
K. Write down the date, time since disconnecting the last time you charged your high voltage battery, and of course write down the 12v battery voltage.
