Shorter Use Times

• As a laptop battery starts to deteriorate, you will often begin to notice that it holds a charge for shorter periods. When the amount of time you can spend on the laptop with it unplugged becomes shorter and shorter, this is a "telltale sign" of laptop battery failing, according to Microsoft.
  
  

Shorter Recharge Times

• If a laptop battery is taking progressively shorter times to recharge, this is a sign that the battery may be going bad. While it may charge very quickly, this generally corresponds to an inability to hold a charge for any significant period of time.
  
  

Unexpectedly Powering Off

• A laptop that enters hibernation mode unexpectedly or suddenly powers off for no discernible reason may have a failing battery. A failing laptop battery can unexpected power off even if the laptop's battery meter shows around 70 or 80 percent power remaining, says Microsoft.
  
  

Low Battery Notification

• Windows 7 displays a notification on the battery meter when the battery is functioning at around 40 percent of its full capacity. The notification, which informs you that the battery might be going bad, was introduced as a new feature in Windows 7.
  
  If the battery needs to be replaced, don't just throw it in the garbage. Laptop batteries are very toxic--follow your computer manufacturer's disposal instructions.