Why my phone battery has four terminal? what is the use of the fourth? I have a LG Optimus One (P500). For sometime I am wondering why my phone's battery has four terminals. I am aware that two terminals are for the positive and negative points and the the third connects to the battery's internal thermistor to monitor its temperature. Still that leaves me puzzled with what the fourth terminal could be for?

Interestingly my phone has only three terminal where as the battery has four. I have searched for answers in Google but no useful results other than description about temperature monitoring comes up.

Also since another doubt also lies in the same image, what is the port that is marked as "A" in the following image? It appears to me as some sort connector and my guess is that it is a connector to a cable with which manufacturers can access something deep in hardware. The Nokia phones which I had also had this feature and I guess this should be common for all phone then.



Update: I am more keen on knowing what the fourth terminal on the battery does rather than why there are three in phone and four in battery. As @Axeman said, this battery could be used in other phones (of LG) as well.
Connector A seems a U.FL-R-SMT-10 and probably is for an external/additional antenna.


  U.FL, is a miniature coaxial RF connector for high-frequency signals
  up to 6 GHz manufactured by Hirose Electric Group in Japan.1 U.FL
  connectors are commonly used inside laptops and embedded systems to
  connect the Wi-Fi antenna to a Mini PCI card. Female U.FL connectors
  are not designed with reconnection in mind, and they are only rated
  for a few reconnects before replacement is needed. The female U.FL
  connectors are generally not sold separately, but rather as part of a
  pigtail with a high-quality 1.32 mm doubly shielded cable, which
  allows for a low-loss connection.


(from Wikipedia)