\documentclass[border = 1mm]{standalone}
\usepackage[utf8]{inputenc}
\usepackage{siunitx}
\usepackage[european, straightvoltages, RPvoltages]{circuitikz}
\usetikzlibrary{babel}
\begin{document}
\begin{circuitikz}[scale=1, transform shape]
\ctikzset{voltage/shift=0,
voltage/distance from node=0.8,
voltage/american plus=\textcolor{red}{$\oplus$},
voltage/american minus=\textcolor{blue}{$\ominus$}}
%
\draw (0,0) to[rmeter, t=G, ,v=\empty] (4,0);
\draw (0,0) to[rmeter, t=G, ,v=$U$,american voltages] (4,0);
%
\draw (0,4) to[rmeter, t=G,v=\empty,t=G,american voltages] (0,0);
\draw (0,4) to[rmeter, t=G,v=\mbox{$U=\SI{10}{V}$},t=G] (0,0);
%
\ctikzset{voltage/shift=0,
voltage/distance from node=5,
voltage/american plus=\textcolor{red}{$\oplus$},
voltage/american minus=\textcolor{blue}{$\ominus$}}
%
\draw (4,0) to[battery1,v_=\empty,american voltages] (4,4);
\draw (4,0) to[battery1,v_=$U$] (4,4);
%
\ctikzset{voltage/shift=2,
voltage/distance from node=100,
voltage/american plus=\textcolor{red}{$\oplus$},
voltage/american minus=\textcolor{blue}{$\ominus$}}
%
\draw (4,4) to[battery1, v_=\empty] (0,4);
\draw (4,4) to[battery1, v_=\empty,american voltages] (0,4);
%\draw (4,4) to[battery1, v=\empty,american voltages,european voltages] (0,4);
% la dernière option l'emporte, il ne fait pas les deux.
%
\end{circuitikz}
\end{document}