Is a voltage regulator the solution?

My friend has a problem with a project he is making.

He is making a useless box - the kind where you filp a switch and the lid opens and a furry arm reaches out at switches the swich off again.
The box is powered by ordinary batteries and the arm is moved by a servo. To control the movements he uses an arduino board.

After a relatively short period of time the arm moves slower and soon the moving parts are out of sync.

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