How long does our battery last????
#26
MBWorld Fanatic!
..."When measuring SoC by open circuit voltage, the battery voltage must be truly 'floating' with no load present. Installed in a car, the parasitic load present makes this a closed circuit voltage (CCV) condition that will falsify the readings. Adjustments must be made when measuring SoC in the CCV state by including the load current in the calculation. In spite of the notorious inaccuracies, most SoC measurements rely on the voltage method because it’s simple."...
#27
MBWorld Fanatic!
#28
MBWorld Fanatic!
I have tested the "parasitic" drain on two of the cars I used to have. These cars did not have all the "gizmos" that this E has so there was no possible harm done by disconnecting the battery.
I simply took the cable of the negative battery terminal off and connected my digital Fluke between the terminal and the cable and measured the amps the car draws when everything is off. After figuring that the automatic hood light was messing with my results and disabling it I got 0.05A pull on both of these cars.
How much would that lower the "rest" voltage of the battery if it is connected in the car?
I know these moders cars have more running in the background but this is all modern computers and I would not be surprised if they would pull even less "parasitic" load than the older cars I measured.
#29
MBWorld Fanatic!
I'm too lazy to do the math (it's not linear) but to put it in perspective.....our batteries = 85 amps, or 85000 milliAmps. A 50 milliAmp draw = 6/100 of one per cent. That's why the voltage method is used as a quick check. It doesn't account for breakdowns in cells when a lot of current is needed....like starting...but just gives you a battery health check.