Hello Tom....
I am going to go out on a limb and say your batteries are shot.
I see you have a Phantom 2 and that is probably 4 yrs old or older and probably original batteries.
You did not state how old the batteries are.
I have a P2 ver3 + with 4 batteries.
2 are dead...won't charge
the other 2 show 4 greens after charging, but when I start it up and go to lift off, I get the red light and low battery as well.
No replacements that I l know of and those that are selling as new, probably have sitting on the self for years.
I hope others reply with their opinions.