Your secret phone ... the one your significant other doesn't know about. Its your down-low-got-a-chick-on-the-side phone!
"Your phone is ringing."
"That's my bat phone... must be a booty call; wifey calls on the main phone!.... Hello? Hey baby. Sure, same bat time, same bat place? See you soon."
A second phone used for talking to girls beside a wife, fiance or steady girlfriend.
I just bought a Tracphone aka "a Bat Phone" from Walmart so I won't get caught by my wife talking to this chick.