Electromotive force is equal to internal resistance times current plus resistance of other components in the circuit times current.
$$\varepsilon = rI + RI$$ Therefore: $$V= \varepsilon-rI$$
This graph relates to battery being used up. This means decrease of voltage (why?). According to the graph as voltage decreases, current increases. The only way I can explain it using the equation V=e-rI is that for some reason internal resistance r increases and as eloctromotive force stays the same, this means decrease in voltage V so both sides equal each other again. But wait! According to the graph current was supposed to increase and the above reasoning doesn't account for that. Please explain in your own words step by step how you can explain this graph using the equation V=e-rI.