1) Which is better battery with cells in series or battery with cells in parallel ?

When n identical cells each of emf ε and internal resistance r are connected in parallel, the total emf of the cells is ε.
When n identical cells each of emf ε  are connected in series, the total emf of the cells is n ε.
So, we can conclude that the combination of cells in series is better than the combination of cells in parallel connection.