Will a small digital meter work for battery voltage?

Panel lights are called IDOT lights after all. My father often tells me that his panel says that he is fully charged, my DVM says he is at +-70%. Go figure, his WFCO charges at 13.5V. OTOH, I charge at 14.55 and rely on the .0x significant digit. I want to know if I am at 80% or 85% SOC. Depending on the plug in meter, they will show that I am at 50% to 100% SOC. Accurate data is king. ...Yes, I do monitor Amp Hours, home brew.

73,
K2LED