If my car won't start and I take my neighbor's battery, what offense am I committing?

The correct offense in this scenario is theft. When you take your neighbor's battery without permission, you are unlawfully taking someone else's property with the intent to deprive them of it. This action fits the definition of theft, as it involves taking someone else's belongings with the intention of using or keeping them without consent.

Burglary of a vehicle involves unlawfully entering a vehicle with the intent to commit a crime, but in this case, you are not entering the vehicle to commit an additional crime; rather, you are taking a part from it. Unauthorized use of a vehicle refers to using someone else's vehicle without permission, which does not apply here since the issue revolves around a battery, not the vehicle itself. Lastly, possession of stolen property pertains to being in possession of property that you know is stolen; however, the initial act of taking the battery is classified as theft before it leads to possession of stolen property.