Your battery is one of the most important parts of your MacBook Pro, so it's important to know the symptoms of a bad battery. Here are some things to look for:
1. Your MacBook Pro won't hold a charge. This is the most obvious symptom of a bad battery. If your computer only lasts for a few minutes on a full charge, or if it dies completely when you unplug it, then your battery is probably shot.
2. Your MacBook Pro takes forever to charge. If it takes several hours to get your computer up to 100%, then something is wrong with your battery. A good battery should be able to reach a full charge in an hour or two at most.
3. Your MacBook Pro's screen dims randomly or flickers. This can be another sign that your battery is on its last legs. As batteries age, they sometimes start to have trouble powering the screen properly, which can result in random dimming or flickering.
4. You hear strange noises coming from your MacBook Pro's speakers. If you start hearing popping or crackling noises coming from your computer's speakers, it could be due to a failing battery causing power fluctuations within the system.
If you're experiencing any of these symptoms, then it's time to get rid of your old battery and invest in a new one