It really depends on the brand, I definitely don't recommend using Hyperion batteries. There are also several other off brands that aren't all that great.

http://androidforums.com/samsung-ga...eware-hyperion-other-3rd-party-batteries.html

Although, if they are Anker, Mugen Power, or Seidio batteries definitely go for it. (These brands make great batteries.)

 

heard that 3rd party batteries may heat n just explode during charging...also that they might blow off some circuits inside the phone..

how really safe are they? (they can be of any company)