Application of Ohm's law to a single resistor and to a series circuit
If you put two 5ohm resistors in series, then the current flowing will be half of what it was with a single resistor.

With half the current, it takes twice as long to move 1C through the circuit, that is, to have the battery expend 10J of energy through the resistors. The battery is working at half the power, power = rate of doing work.

Each resistor dissipated 5J, that is 5v was required to push 1C through them at the lower current.