The LC charging system has a mind of its own, and I haven’t heard any theory that correctly describes the charge/discharge algorithm. Here’s a Victron Smartshunt record of battery voltage (blue line) and battery state of charge (SoC, red line). State of charge measured by the shunt tracks all current into and out of the battery. As I described in another post on this forum, it is much more accurate than merely measuring battery voltage to estimate SoC.
The record shows 4 days of data, starting after I charged the battery with a Noco charger. The spiky voltages at the right were when I drove the vehicle. This caused the battery voltage to fluctuate between higher and lower voltages, but the net result was to decrease the SoC from ~94% to ~88%, while simultaneously increasing so-called “surface charge” by perhaps a tenth of a volt or so. (This increase was mostly gone by the right side of the record, after the battery had a chance to rest.) Evidently, the battery was being drained faster than being charged while driving.
This record has a couple lessons for us. For those of us, like myself, who had been obsessed with whether switching to an AGM would result in the battery charging at optimal charging profile, the data suggest that the oem battery itself isn’t charged with an optimal profile.
Second, driving doesn’t necessarily increase battery SoC, particularly if voltage is high from an external charger.
My tentative hunch from looking at such data is that the charging algorithm prioritizes keeping the battery from draining “too much” rather than at optimum SoC.
