Measuring battery load and charge

Is there simple way to read the battery load with Arduino? I read other posts, and it appears my options are:

  1. Shift voltage with resistor divider between 0 and 3.3V (or 5V)
  2. Use op-amp to get the shifted and possible scaled output
    here is the schematic of what i want to do:
    Battery load.png

Question 1: If I use method 1, will that disturb the reading of the existing meter?
Question 2: If I need to use method 2, what exactly is the op-amp part and schematic I should use?

Battery load.png

Arduino can only measure voltage, you appear to intend to measure the voltage across a shunt resistor (altho the battery is shown with its + - terminals swapped).
For very low voltages, you'll probably want to amplify the signal before bringing it into an analogInput. Or, use an external ADC, say 12 bits or 14 bits, that can provide 1mV or ~0.25V resolution over 5V with no amplification needed.

(altho the battery is shown with its + - terminals swapped).

Sorry about that.. Fixed!

For very low voltages, you'll probably want to amplify the signal before bringing it into an analogInput. Or, use an external ADC, say 12 bits or 14 bits, that can provide 1mV or ~0.25V resolution over 5V with no amplification needed

I actually plan to use Teensy3.2 which should be able to do ADC @ 14bits.

My questions still stand:
Question 1: If I use method 1, will that disturb the reading of the existing meter?
Question 2: If I need to use method 2, what exactly is the op-amp part and schematic I should use?
I don't have much experience lately so I want to make sure I do the right thing here..

If you have a 14-bit ADC already, just use it. No need to mess with external opamp. I can't recommend a current part, have not used an op amp in quite a while.

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If you have a 14-bit ADC already, just use it. No need to mess with external opamp. I can't recommend a current part, have not used an op amp in quite a while

If I use it how do i measure battery discharge? the voltage across the shunt will be negative. If I shift it with resistor divider from ground to +5v, i'm thinking that this could screw-up the reading of the existing meter as it will change the potential across the shunt. Or will it?