lipo battery boot issue

[Ghost]

When my board failed to boot using the power supply, I tried giving input through the battery terminal, by changing the jumper settings 

      using an smps, but nothing happened, even the LED did not go high which was happening with the normal power supply. 
  
      One more thing noticed is there are 3 terminals for the lipo power provided on the board, bu we get lipo with only two terminals. I don't know why there is a pin in the center and what does it do. 

 
Hello, 

I'm just the messenger of the encountered issue - it was brought to by attention by Arffeh, who asked me to create this post. From what he wrote to me it transpires that a drained or partially drained battery can can cause a failed boot  even if the board is connected to the mains. 

He wrote:
"A completely dead lipo when connected, with the jumper correctly set, causes a failure to boot when correct power is applied (...). I'm talking about using actual normal power, with the battery just chilling out (...) Shouldn't cause a full failure to boot, but yeah. The battery is able to affect the 2.1 amp input (...) [I] plucked the battery and reapplied power [and it boot correctly]". 

Has anyone else encountered a similar problem or has a suggestion of how to resolve this ? 

Cheers

Third pin on Lipo battery is related to internal temperature sensing, I believe - a safety mechanism during charging.