I've used MS View to capture my MS MPPT 60 data. And that also means that I have laptop draws as part of the equation. The Rasberry Pi is interesting and offers a much lower power consumption method of data collecting.
I'm not really concerned about accuracy for 2 reasons:
1. Unless you have a remote voltage battery sense you're measuring CC output voltage, not battery voltage.
2. Unless the house loads are 0.00A you're not measuring battery amps any way but rather house loads and battery amps.
But great progress on the Rasberry!