Simplest battery monitor and shunt? Advice for non-expert

I bought a Victron smart shunt and I monitor my batteries daily..I can tell you this,too the tenth my other voltage meters, as cheap as the cigarette lighter plugins and the voltage meter on my battery boxes,are pretty close to the Victron readings,but there only to the tenth and not one hundreths...Now that I know that,I feel confident in there readings..

Jayco