Where did you take the 12.1volt reading from? Measuring at the battery directly, 12.1 volts is only about a 40% charge. If your battery is settling at that voltage over night after a good long drive then that indicates battery issues. I don't know about your voltage drop readings but they don't seem good either.@gti16vman Awesome! Thanks for the link, super helpful.
I got the gauge programmed but haven't tested it yet actually going anywhere. Reads 15 in reverse, 1 in Drive, 0 in park/neutral.
Before getting it set up though, I snagged my dad's meter (and my dad) take some battery measurements. Started the vehicle from cold, sitting overnight, with 47F ambient temperature. Turned the truck on twice, with the voltage drop measured at 9.884V and 9.54V on the sequential starts. The cold battery hung out at 12.146V and the alternator kept it up at 14.266.
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I also took 3 short trips of 15, 1, and 14 miles, all with no issues. I mean, who doesn't like to chase intermittent problems?