amperage/voltage long period datalogging/oscilloscope

Hi guys, im considering making a shield for an ardunio uno to datalog the voltage and amperage of a car battery. The reason im trying to make this device is so i can see when and how much amperage is being drawn off of a car battery after it has been sitting for a couple of hours. This is a random draw and im thinking that if i could match the time signature while datalogging, to the amperage drop i might be able to narrow down what exactly the issue is.

So im looking for advice on how to approach this, the three main features i would like is:

datalogging for over 8+ hours on an sd card at around 30sec -1 minute intervals
voltage and amperage logging in milivolt incriments/miliamp
powered by same car battery

i found a couple of 50a current sensing shields that were based on the ACS758 chip and the holzer effect, would this application be better suited to the hall effect sensor instead?

Secondly, how could i program this to have a clock that keeps time and can be printed out with the referenced voltage/amperage readings on to the sd card?

thanks for the help.

Is this battery in a car? You can get a few-hundred amps when starting so a series current sensor could be a problem (unless you disconnect the current sensor when you're done with the test).

voltage and amperage logging in milivolt incriments/miliamp

The Arduino's 10-bit ADC counts from 0-1023 so it has a resolution of about 1/1000 If you map 0-12V to 0-1023 you get a resolution of about 12mV. 50A full-scale would be a resolution of about 50mV.

Secondly, how could i program this to have a clock that keeps time

Elapsed time is fairly easy with millis() which you could convert to minutes or hours & minutes. If you want time-of-day, you'll need a real-time clock module.

and can be printed out with the referenced voltage/amperage readings on to the sd card?

I've never used an SDcard...

It might just be easier to connect a laptop and capture the readings to the serial monitor. I have done something like that before, "printing" elapsed seconds and some readings. I probably didn't capture 500 readings but I was able to scroll & copy from the window into Notepad. (I didn't try copying into Excel.)

thanks for the reply, this was meant to be used only when the vehicle is parked and not running or starting as i would assume it would melt the shunt in a very quick order. Mainly just to diagnose parasitic draw issues with multiple vehicles i have.

Ah ok so the ADC counts are right around 1000, so i could theoretically get 25mv increments if a 25a scale was used. im looking for high enough amperage that if i accidentally turn on the radio or accesory that the resulting amp load wont immediately fry the current sensor, while having a fairly high resolution for graphing purposes.

ill have to look into the real time clock module as time is sort of relevant as to when the battery gets drained down to almost dead. Seems almost as if on star or a relay is being commanded on randomly and im trying to narrow down if this is a pattern or a random occurance.

ill try looking around to see what i can find for exporting to an sdcard and excel, thanks for the tips.