The car won't start because its battery, or it's battery, is dead?
How to Remember It:
The word it's means "it is" or "it has," while its means "belonging to it."
In the sentence above, "it is battery" or "it has battery" doesn't work so the correct version has to be its.
Similarly, in the sign shown here, "it is/has accessories" and "it is/has enclosure" don't make sense, so it's wasn't the right choice.
Image courtesy of Karlonia.com