German sports car maker Porsche (<a href="https://www.boerse-frankfurt.de/equity/porsche-ag-vz" target="_blank">ETR:P911</a>) has signed an agreement to make a majority investment in Varta AG’s (<a href="https://www.boerse-frankfurt.de/equity/varta-ag" target="_blank">ETR:VAR1</a>) large-format lithium-ion round cells business, the struggling battery maker said on Wednesday.