Hi! I’m really new to all of this and trying to solve a strange problem.
We have a couple of systems set up, with a PV, a 12V car battery and a load (datalogger and turbidity sonde) attached to a MPPT 75/10.
It was all working fine for some time - see attached photo. You see solar power go up and down every day, as well as battery voltage.
Then, everything flatlines for a while, then it all died. Since then the system has come back intermittantly, but the battery voltage is all over the shop, frequently dropping to zero. But when i measure the actual voltage across the battery, it is 12!
What might have happened? Have I fried things somehow? As a novice i really appreciate any help anyone can give me 
