If your car has been getting hard to start, the problem might not be the battery itself, but corrosion on the battery terminals. Knowing how to clean battery terminals could save you the cost of a new battery. The corrosion can be quite acidic so it's a good idea to wear gloves and eye protection.
The first step when cleaning battery terminals is to remove the cables from the battery. Connect a battery saver if you have one to save your radio presets and other settings following the instructions provided with the device. If you do not have a memory saver make sure that you have any PIN numbers required for the radio or other equipment in your car.
Starting with the negative cable (usually black and marked with a '-') remove the cable by loosening the nut or bolt and then twisting the terminal back and forth while lifting it off the battery post. Tuck the terminal out of the way where it won't touch either battery post, the body of the car, or the other terminal. Repeat the process for the positive cable (usually red and marked with a '+').