Student or Learner
Take out the batteries from camera when is it not in use for a period.
The batteries will leak if you didn't take it out and it will harm your camera.
Is the "leak" use correctly?
Yes, but the rest of the sentence is wrong. You used "the batteries" (plural) so "take it out" and "it will harm" are wrong. Can you see why? Try to rewrite the sentences so that the verbs agree with the subject.
In case of confusion, "battery" is singular and "batteries" is plural.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.