If you notice these issues, then it's time to replace the battery: 1. If the battery ends have completely corroded or are damaged in any way 2. If the battery casing has a fissure or is oozing 3. When the battery casing is sticking out – commonly caused by stowing or running it in excessively sultry temperatures 4. If the battery acid level is low. It’ll expose the inner plates to the air and, therefore, they’ll instantly sulfate. 5. If the battery wasn’t charged correctly. It’s mostly caused by cheap charger settings. 6. When the battery can no longer maintain a charge. It’s commonly caused by sulfation after a long period of inactivity (insufficient maintenance of the charge level).