How do I know when the rechargeable battery is at the end of its usable life? 

" Although fully charging the battery, it still ran out of battery in a short time.", " The battery has been charged for a long time, but still can't be fully charged." 
  Have you ever encountered those kinds of situations in the daily life? Before disposing of the batteries, let's learn about how to check the condition of the batteries. 
 How Do I Know When the Rechargeable Battery's Service Life Has Ended?
The occurrence of the symptoms below could indicate that your rechargeable batteries need replacing. 
  • The battery has been used extensively over the last few years and its operating time has started to decrease after charging.
  • If the charging of one battery poses a lot of difficulties e.g. when the charging time becomes increasingly longer.
  However, in the case of the defects below, the main cause could be an intermittent contact between battery and terminal.
  • Battery charge is never completed or takes a large amount of time (guideline: 2 to 3 times longer than normal charging time).
  • When the operating time is noticeably short despite having used the battery only a few times.
  In the cases above, it is recommended to clean the plus and minus terminals of the batteries, and the terminals of the charger with a cleaning cloth.
Rechargeable Battery Usage Tips: How to Use a Rechargeable Battery Properly? 
1. Use the right battery: 
This one goes without saying: if your device needs AA batteries, use AA batteries only. Do not try using smaller batteries, as this could lead to imperfect contact. (Read more about which is: Guide to Rechargeable Batteries: How Does It Work and How to Choose Wisely?
2. Don't mix and match: 
  If your device needs two or more batteries, always use the same type. Don’t mix up old and new batteries. If possible, only use batteries from the same package (and expiration date). Never use different brands in the same device, as different brands have a different battery composition and a different power level.
3.  Store when needed:
  • Keep batteries away from direct sunlight and children.
  • Make sure not to allow any moisture near the batteries.
  If they’re stored correctly, batteries generally retain their power for a long time. That’s why it’s important to store whenever you need to. If you plan on not using a device for a longer period of time, be sure to remove the batteries.